Extract babel config into a .babelrc file

[psevcenco-ellation]

Note: This part is already inluded in a much larger Various improvements PR. However that PR seems to be stale. It might be easier to merge this very simple fix as a separate PR.

Summary: If anyone tries to pipe current version of unescape-js through babel with custom config they will be unable to do so since the local babel config placed inside the package.json will take precedence over any other config.
This is not ideal as not everyone excludes node_modules when running babel.
The fix is very simple: extract babel config into a .babelrc file and exclude this file when publishing to npm.

[coveralls]

Coverage remained the same at 100.0% when pulling 06bfaaf on psevcenco-ellation:extract-babel into 7546fb1 on iamakulov:master.

[iamakulov]

Thanks :) Just published as @1.1.1!

[psevcenco-ellation]

Thanks :) Just published as 1.1.1!

Thank you! Already using it :)