.travis.yml in twilio-ruby-5.2.1 vs .travis.yml in twilio-ruby-5.2.2

@@ -1,13 +1,20 @@
 sudo: false
 language: ruby
 cache: bundler
 bundler_args: --without development
+
 rvm:
   - ruby-head
   - 2.4.0
   - 2.3.0
   - 2.2.0
   - 2.1
   - 2.0.0
+
 matrix:
   fast_finish: true
+
+before_install:
+  # Bundler on Travis may be too out of date
+  # Update bundler to a recent version.
+  - gem install bundler