Bump rollbar from 2.19.4 to 2.20.1 (#245)

Bumps [rollbar](https://github.com/rollbar/rollbar-gem) from 2.19.4 to 2.20.1.
- [Release notes](https://github.com/rollbar/rollbar-gem/releases)
- [Changelog](https://github.com/rollbar/rollbar-gem/blob/master/CHANGELOG.md)
- [Commits](rollbar/rollbar-gem@v2.19.4...v2.20.1)

Gemfile.lock

@@ -215,7 +215,7 @@ GEM
     responders (1.1.2)
       railties (>= 3.2, < 4.2)
     rolify (5.2.0)
-    rollbar (2.19.4)
+    rollbar (2.20.1)
       multi_json
     rspec (3.5.0)
       rspec-core (~> 3.5.0)