Install the same bundler in travis that we use in the omnibus build

2.0 requires rubygems 3.0 and we want rubygems to match what we build in
the omnibus package.

Signed-off-by: Tim Smith <tsmith@chef.io>

.travis.yml

@@ -11,7 +11,7 @@ addons:
 # Early warning system to catch if Rubygems breaks something
 before_install:
   - gem update --system $(grep rubygems omnibus_overrides.rb | cut -d'"' -f2)
-  - gem install bundler # https://github.com/travis-ci/travis-ci/issues/8969
+  - gem install bundler --version $(grep bundler omnibus_overrides.rb | cut -d'"' -f2) # https://github.com/travis-ci/travis-ci/issues/8969
   - gem --version
   - rm -f .bundle/config