Bump ffi from 1.9.18 to 1.11.3

Bumps [ffi](https://github.com/ffi/ffi) from 1.9.18 to 1.11.3.
- [Release notes](https://github.com/ffi/ffi/releases)
- [Changelog](https://github.com/ffi/ffi/blob/master/CHANGELOG.md)
- [Commits](ffi/ffi@1.9.18...1.11.3)

Signed-off-by: dependabot[bot] <support@github.com>

Author: dependabot[bot]

Gemfile.lock

@@ -65,7 +65,7 @@ GEM
       warden (~> 1.2.3)
     erubis (2.7.0)
     execjs (2.7.0)
-    ffi (1.9.18)
+    ffi (1.11.3)
     globalid (0.4.0)
       activesupport (>= 4.2.0)
     haml (5.0.1)