Bump ffi from 1.9.18 to 1.12.2

Bumps [ffi](https://github.com/ffi/ffi) from 1.9.18 to 1.12.2.
- [Release notes](https://github.com/ffi/ffi/releases)
- [Changelog](https://github.com/ffi/ffi/blob/master/CHANGELOG.md)
- [Commits](ffi/ffi@1.9.18...1.12.2)

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

Gemfile.lock

@@ -89,7 +89,7 @@ GEM
     execjs (2.7.0)
     faraday (0.17.3)
       multipart-post (>= 1.2, < 3)
-    ffi (1.9.18)
+    ffi (1.12.2)
     fog-aws (2.0.0)
       fog-core (~> 1.38)
       fog-json (~> 1.0)
@@ -144,6 +144,7 @@ GEM
     kaminari-mongoid (1.0.1)
       kaminari-core (~> 1.0)
       mongoid
+    libv8 (3.16.14.19)
     loofah (2.1.1)
       crass (~> 1.0.2)
       nokogiri (>= 1.5.9)
@@ -252,6 +253,7 @@ GEM
     rb-inotify (0.9.10)
       ffi (>= 0.5.0, < 2)
     rdiscount (2.2.0.1)
+    ref (2.0.0)
     rubocop (0.51.0)
       parallel (~> 1.10)
       parser (>= 2.3.3.1, < 3.0)
@@ -293,6 +295,9 @@ GEM
       tins (~> 1.0)
     test-unit (3.2.6)
       power_assert
+    therubyracer (0.12.3)
+      libv8 (~> 3.16.14.15)
+      ref
     thor (0.19.4)
     thread_safe (0.3.6)
     tilt (2.0.8)
@@ -359,6 +364,7 @@ DEPENDENCIES
   simplecov
   sucker_punch (~> 2.0)
   test-unit (~> 3.0)
+  therubyracer
   twitter
   uglifier (>= 1.0.3)