Adopt Standard Source Map Naming

[bdkjones]

Currently, if you have a file named input.jsx and you compile it to output.js and enable the source-map option, you'll get a source map file named output.js.mapping.

The defacto industry standard naming convention for source maps is [output filename].[output extension].map. In this example, the source map should be output.js.map.

Please move to that naming convention, as it matches what literally every other language does. Sass, CoffeeScript, Less, Stylus and Uglify.js just off the top of my head.