Handle feed burner xhtml atom feeds
Add specs for Preprocessor

Also, remove redundant outer loop specs.
Make RBX work on Travis

Also, remove the rbx group of gems - no longer needed.
Bump loofah gem to 2.0.0
Bump version for 1.3.0
Update CHANGELOG for 1.3.0

[skip ci]
Merge remote-tracking branch 'upstream/master'

Conflicts:
	lib/feedjira/parser/atom.rb
	spec/sample_feeds.rb