Bump ffi from 1.9.6 to 1.13.1

Bumps [ffi](https://github.com/ffi/ffi) from 1.9.6 to 1.13.1.
- [Release notes](https://github.com/ffi/ffi/releases)
- [Changelog](https://github.com/ffi/ffi/blob/master/CHANGELOG.md)
- [Commits](ffi/ffi@v1.9.6...1.13.1)

Signed-off-by: dependabot[bot] <[email protected]>

Author: dependabot[bot]

Gemfile.lock

@@ -38,7 +38,7 @@ GEM
     fauxhai (2.2.0)
       net-ssh
       ohai
-    ffi (1.9.6)
+    ffi (1.13.1)
     ffi-yajl (1.2.0)
       ffi (~> 1.5)
       libyajl2 (~> 1.0)
@@ -91,7 +91,7 @@ GEM
     mixlib-cli (1.5.0)
     mixlib-config (2.1.0)
     mixlib-log (1.6.0)
-    mixlib-shellout (1.6.0)
+    mixlib-shellout (1.6.1)
     multi_json (1.10.1)
     net-scp (1.2.1)
       net-ssh (>= 2.6.5)