[FIXUP] s/after_install/install

Avoid doing a `bundle install` since it isn't necessary

Author: NickLaMuro

.travis.yml

@@ -14,7 +14,7 @@ env:
     - RVM_RUBY_VERSION=2.6
     - RVM_RUBY_VERSION=ruby-head
 
-after_install:
+install:
 - bundle exec rake test:docker:$RVM_RUBY_VERSION:build
 
 script: