Update rspec_focus plugin to support new JSON-style hash syntax

Update rspec_focus plugin to support new JSON-style hash syntax.
Additionally, it should ignore mention of :focus within spec code blocks
Possibly not, but the check needs some way of distinguishing a `:focus` in the line starting a describe/context/example block from one within the block itself.

Perhaps something more flexible than `grep` is required in this case? Maybe something like `Ripper` which has been distributed with Ruby since 1.9? Although you'd then need to parse all ruby files under the test/spec directories, rather than just the files being committed?