Skip installing gem docs

JRuby stalls installing docs

  $ script/update_rubygems_and_install_bundler

  Updating rubygems-update
  Fetching rubygems-update-3.1.4.gem
  Successfully installed rubygems-update-3.1.4
  Parsing documentation for rubygems-update-3.1.4
  Installing ri documentation for rubygems-update-3.1.4

  No output has been received in the last 10m0s, this potentially indicates a stalled build or something wrong with the build itself.
  Check the details on how to adjust your build configuration on: https://docs.travis-ci.com/user/common-build-problems/#build-times-out-because-no-output-was-received

  The build has been terminated

script/update_rubygems_and_install_bundler

@@ -4,5 +4,5 @@
 
 set -e
 
-yes | gem update --system
-yes | gem install bundler
+yes | gem update --system --no-document
+yes | gem install bundler --no-document