Bump ffi from 1.9.6 to 1.11.1

Bumps [ffi](https://github.com/ffi/ffi) from 1.9.6 to 1.11.1.
- [Release notes](https://github.com/ffi/ffi/releases)
- [Changelog](https://github.com/ffi/ffi/blob/master/CHANGELOG.md)
- [Commits](ffi/ffi@v1.9.6...1.11.1)

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

Author: dependabot[bot]

Gemfile.lock

@@ -15,7 +15,7 @@ GEM
       eventmachine (>= 0.12.9)
       http_parser.rb (~> 0.6.0)
     eventmachine (1.0.8)
-    ffi (1.9.6)
+    ffi (1.11.1)
     formatador (0.2.5)
     guard (2.6.1)
       formatador (>= 0.2.4)
@@ -79,7 +79,7 @@ GEM
     thor (0.19.1)
     timers (4.0.1)
       hitimes
-    yajl-ruby (1.3.0)
+    yajl-ruby (1.1.0)
 
 PLATFORMS
   ruby