Bump ffi from 1.9.21 to 1.12.1 (#233)

Bumps [ffi](https://github.com/ffi/ffi) from 1.9.21 to 1.12.1.
- [Release notes](https://github.com/ffi/ffi/releases)
- [Changelog](https://github.com/ffi/ffi/blob/master/CHANGELOG.md)
- [Commits](ffi/ffi@1.9.21...1.12.1)

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

Author: dependabot[bot]

Gemfile.lock

@@ -3,7 +3,7 @@ GEM
   specs:
     builder (3.2.3)
     erubis (2.7.0)
-    ffi (1.9.21)
+    ffi (1.12.1)
     gssapi (1.2.0)
       ffi (>= 1.0.1)
     gyoku (1.3.1)