Update dev deps and add source map for .min dist file
Peg intl-messageformat to 1.0.0-rc-6
Remove use of `indexOf()` from locale resolving

This removes the use of `Array.prototype.indexOf()`, an ES5 method,
from this package. This also simplifies how the locale data is stored.

Relates to intl-messageformat#76
Merge pull request #4 from ericf/rm-indexof

Remove use of `indexOf()` from locale resolving