Unset RUBYOPT instead of re-enabling rubygems.

The old code does not work on Ruby 2.5.

Author: myronmarston

travis/script/functions.sh

@@ -80,11 +80,7 @@ function run_spec_suite_for {
       pushd ../$1
       unset BUNDLE_GEMFILE
       bundle_install_flags=`cat .travis.yml | grep bundler_args | tr -d '"' | grep -o " .*"`
-      if is_mri_192_plus; then
-        travis_retry eval "RUBYOPT=$RUBYOPT:'--enable rubygems' bundle install $bundle_install_flags"
-      else
-        travis_retry eval "bundle install $bundle_install_flags"
-      fi
+      travis_retry eval "(unset RUBYOPT; exec bundle install $bundle_install_flags)"
       run_specs_and_record_done
       popd
     else