Move the cursor to the enclosing brace if no brace is selected.

Modify the `bracket-matcher:go-to-matching-bracket` event (the `goToMatchingPair` function) so that if the cursor is not adjacent to a brace, the cursor is instead moved to just before the enclosing start brace (if one exists). Only matches `{}` braces at the moment.

Inspired by the vim `[{` command.

Theoretically this could be a different event/command, but I think that adding this to the existing function will be one less thing for a developer to remember, particularly since the behavior it's replacing is a noop. I'm welcome to dissenting opinions, of course. :-) It could even be a different plugin altogether! atom-match-enclosing or some such.