Backport changelog fixed from #11713 [ci skip]
Merge pull request #11714 from jetthoughts/11706_remove_bad_override_of_xml

Removed redundant xml override from pg adapter
Conflicts:
	activerecord/CHANGELOG.md
Use assert_nil instead of testing for equality
Merge pull request #11455 from antonio/fix_enable_extension_not_being_defined

Define enable_extension method to prevent undefined method error
Merge pull request #11716 from jetthoughts/use_backquote_for_terms_in_getting_strated

Replaced quotation marks for term by apostrophes in getting started guide [ci skip]
Enable jruby and rubinius on travis