Update rubygems before bundler
Update rubygems before bundler

Fixes issues w/ Travis & Ruby 2.5 https://github.com/travis-ci/travis-ci/issues/8978#issuecomment-354036443
antstorm/money-rails,antstorm/money-rails,RubyMoney/money-rails,antstorm/money-rails,RubyMoney/money-rails,RubyMoney/money-rails