fix(package): update socket.io to version 1.7.3

Closes #75

https://greenkeeper.io/

Author: greenkeeper[bot]

package.json

@@ -26,7 +26,7 @@
     "minimist": "^1.2.0",
     "node-static": "^0.7.7",
     "semver": "^5.1.0",
-    "socket.io": "~1.6.0",
+    "socket.io": "~1.7.3",
     "string-format": "~0.5.0"
   },
   "devDependencies": {