Change CSS to JS in spec

Looks like it was a holdover from the jekyll/jekyll-sass-converter spec.
Remove deprecated config property

treat_symbols_as_metadata_keys_with_true_values is deprecated. Per RSpec:

RSpec::Core::Configuration#treat_symbols_as_metadata_keys_with_true_values= is deprecated, it is now set to true as default and setting it to false has no effect.
Change Matching Regex to use standard symbols

For beginning and end of line, ^ and $.
And added i flag for case insensitivity.

This also more closely matches the sass/scss converters
Merge pull request #6 from rodaine/master