invert rubocop env test in travis config
add rails.png to test images
add testing railtie to travis config
add rails to Gemfile conditionally

version from ENV['RAILS_VERSION'] if it is present
create rails application dynamically in railtie_spec
add railtie initialisation specs
cleanup app assets config
add passing options specs
move nrmse and flatten_animation to spec_helper
move be_smaller_than and be_similar_to matchers to spec_helper
add assets optimising specs
group assets config in dummy app initialisation
move rubocop travis test to the end
add changelog entry, resolved #73
Merge branch 'railtie-spec'