Don't add '.js' extension if the source file doesn't have an extension

[christophercrouzet]

Hello!

I have in my current project a bin folder containing executable files without any extension, and I ran into the issue where these files were renamed with a .js extension after going through gulp-babel when I wished they could remain extensionless.

I've made a quick change to fix this but, as it causes a change of behaviour, this might possibly break for some users that relied on this feature for their executable files.

To keep backward compatibility, a new option could be added, possibly accepting globs as values, that would allow to filter which files are to be renamed to .js, and that would come with a default value preserving the current behaviour. I could have modified the opts parameter in this purpose but didn't dare doing so since it should remain dedicated to Babel but maybe adding a second parameter to gulp-babel could do?

Let me know!

Kind regards.