diff --git a/package.json b/package.json
index cc2a071..afb1448 100644
--- a/package.json
+++ b/package.json
@@ -17,6 +17,6 @@
   },
   "homepage": "https://github.com/yllg/Algorithms-JS#readme",
   "devDependencies": {
-    "koa": "^2.13.1"
+    "koa": "^2.15.4"
   }
 }
diff --git a/yarn.lock b/yarn.lock
index 0cdad56..4ba7b51 100644
--- a/yarn.lock
+++ b/yarn.lock
@@ -10,11 +10,6 @@ accepts@^1.3.5:
     mime-types "~2.1.24"
     negotiator "0.6.2"
 
-any-promise@^1.1.0:
-  version "1.3.0"
-  resolved "https://registry.yarnpkg.com/any-promise/-/any-promise-1.3.0.tgz#abc6afeedcea52e809cdc0376aed3ce39635d17f"
-  integrity sha1-q8av7tzqUugJzcA3au0845Y10X8=
-
 cache-content-type@^1.0.0:
   version "1.0.1"
   resolved "https://registry.yarnpkg.com/cache-content-type/-/cache-content-type-1.0.1.tgz#035cde2b08ee2129f4a8315ea8f00a00dba1453c"
@@ -40,20 +35,20 @@ content-type@^1.0.4:
   resolved "https://registry.yarnpkg.com/content-type/-/content-type-1.0.4.tgz#e138cc75e040c727b1966fe5e5f8c9aee256fe3b"
   integrity sha512-hIP3EEPs8tB9AT1L+NUqtwOAps4mk2Zob89MWXMHjHWg9milF/j4osnnQLXBCBFBk/tvIG/tUc9mOUJiPBhPXA==
 
-cookies@~0.8.0:
-  version "0.8.0"
-  resolved "https://registry.yarnpkg.com/cookies/-/cookies-0.8.0.tgz#1293ce4b391740a8406e3c9870e828c4b54f3f90"
-  integrity sha512-8aPsApQfebXnuI+537McwYsDtjVxGm8gTIzQI3FDW6t5t/DAhERxtnbEPN/8RX+uZthoz4eCOgloXaE5cYyNow==
+cookies@~0.9.0:
+  version "0.9.1"
+  resolved "https://registry.yarnpkg.com/cookies/-/cookies-0.9.1.tgz#3ffed6f60bb4fb5f146feeedba50acc418af67e3"
+  integrity sha512-TG2hpqe4ELx54QER/S3HQ9SRVnQnGBtKUz5bLQWtYAQ+o6GpgMs6sYUvaiJjVxb+UXwhRhAEP3m7LbsIZ77Hmw==
   dependencies:
     depd "~2.0.0"
     keygrip "~1.1.0"
 
-debug@~3.1.0:
-  version "3.1.0"
-  resolved "https://registry.yarnpkg.com/debug/-/debug-3.1.0.tgz#5bb5a0672628b64149566ba16819e61518c67261"
-  integrity sha512-OX8XqP7/1a9cqkxYw2yXss15f26NKWBpDXQd0/uK/KPqdQhxbPa994hnzjcE2VqQpDslf55723cKPUOGSmMY3g==
+debug@^4.3.2:
+  version "4.4.0"
+  resolved "https://registry.yarnpkg.com/debug/-/debug-4.4.0.tgz#2b3f2aea2ffeb776477460267377dc8710faba8a"
+  integrity sha512-6WTZ/IxCY/T6BALoZHaE4ctp9xm+Z5kY/pzYaCHRFeyVhojxlrm+46y68HA6hr0TcwEssoxNiDEUJQjfPZ/RYA==
   dependencies:
-    ms "2.0.0"
+    ms "^2.1.3"
 
 deep-equal@~1.0.1:
   version "1.0.1"
@@ -147,37 +142,30 @@ keygrip@~1.1.0:
   dependencies:
     tsscmp "1.0.6"
 
-koa-compose@^3.0.0:
-  version "3.2.1"
-  resolved "https://registry.yarnpkg.com/koa-compose/-/koa-compose-3.2.1.tgz#a85ccb40b7d986d8e5a345b3a1ace8eabcf54de7"
-  integrity sha1-qFzLQLfZhtjlo0Wzoazo6rz1Tec=
-  dependencies:
-    any-promise "^1.1.0"
-
 koa-compose@^4.1.0:
   version "4.1.0"
   resolved "https://registry.yarnpkg.com/koa-compose/-/koa-compose-4.1.0.tgz#507306b9371901db41121c812e923d0d67d3e877"
   integrity sha512-8ODW8TrDuMYvXRwra/Kh7/rJo9BtOfPc6qO8eAfC80CnCvSjSl0bkRM24X6/XBBEyj0v1nRUQ1LyOy3dbqOWXw==
 
-koa-convert@^1.2.0:
-  version "1.2.0"
-  resolved "https://registry.yarnpkg.com/koa-convert/-/koa-convert-1.2.0.tgz#da40875df49de0539098d1700b50820cebcd21d0"
-  integrity sha1-2kCHXfSd4FOQmNFwC1CCDOvNIdA=
+koa-convert@^2.0.0:
+  version "2.0.0"
+  resolved "https://registry.yarnpkg.com/koa-convert/-/koa-convert-2.0.0.tgz#86a0c44d81d40551bae22fee6709904573eea4f5"
+  integrity sha512-asOvN6bFlSnxewce2e/DK3p4tltyfC4VM7ZwuTuepI7dEQVcvpyFuBcEARu1+Hxg8DIwytce2n7jrZtRlPrARA==
   dependencies:
     co "^4.6.0"
-    koa-compose "^3.0.0"
+    koa-compose "^4.1.0"
 
-koa@^2.13.1:
-  version "2.13.1"
-  resolved "https://registry.yarnpkg.com/koa/-/koa-2.13.1.tgz#6275172875b27bcfe1d454356a5b6b9f5a9b1051"
-  integrity sha512-Lb2Dloc72auj5vK4X4qqL7B5jyDPQaZucc9sR/71byg7ryoD1NCaCm63CShk9ID9quQvDEi1bGR/iGjCG7As3w==
+koa@^2.15.4:
+  version "2.15.4"
+  resolved "https://registry.yarnpkg.com/koa/-/koa-2.15.4.tgz#7000b3d8354558671adb1ba1b1c09bedb5f8da75"
+  integrity sha512-7fNBIdrU2PEgLljXoPWoyY4r1e+ToWCmzS/wwMPbUNs7X+5MMET1ObhJBlUkF5uZG9B6QhM2zS1TsH6adegkiQ==
   dependencies:
     accepts "^1.3.5"
     cache-content-type "^1.0.0"
     content-disposition "~0.5.2"
     content-type "^1.0.4"
-    cookies "~0.8.0"
-    debug "~3.1.0"
+    cookies "~0.9.0"
+    debug "^4.3.2"
     delegates "^1.0.0"
     depd "^2.0.0"
     destroy "^1.0.4"
@@ -188,7 +176,7 @@ koa@^2.13.1:
     http-errors "^1.6.3"
     is-generator-function "^1.0.7"
     koa-compose "^4.1.0"
-    koa-convert "^1.2.0"
+    koa-convert "^2.0.0"
     on-finished "^2.3.0"
     only "~0.0.2"
     parseurl "^1.3.2"
@@ -213,10 +201,10 @@ mime-types@^2.1.18, mime-types@~2.1.24:
   dependencies:
     mime-db "1.48.0"
 
-ms@2.0.0:
-  version "2.0.0"
-  resolved "https://registry.yarnpkg.com/ms/-/ms-2.0.0.tgz#5608aeadfc00be6c2901df5f9861788de0d597c8"
-  integrity sha1-VgiurfwAvmwpAd9fmGF4jeDVl8g=
+ms@^2.1.3:
+  version "2.1.3"
+  resolved "https://registry.yarnpkg.com/ms/-/ms-2.1.3.tgz#574c8138ce1d2b5861f0b44579dbadd60c6615b2"
+  integrity sha512-6FlzubTLZG3J2a/NVCAleEhjzq5oxgHyaCU9yYXvcLsvoVaHJq/s5xXI6/XXP6tz7R9xAOtHnSO/tXtF3WRTlA==
 
 negotiator@0.6.2:
   version "0.6.2"