Only compiling files using ext once despite changes.

[afridley]

grunt.config.merge({
        babel: {
            options: {
                sourceMap: false,
                presets: ['env']
            },
            dist: {
                files: [{
                    expand: true,
                    cwd: '<%= env.DIR_SRC %>/assets/scripts/',
                    src: '**/*.js',
                    ext: '.cmp.js',
                    dest: '<%= env.DIR_SRC %>/assets/scripts/'
                }]
            }
        },

This will compile the .cmp.js files, but any changes to the original js files will yeild no change until the .cmp.js files are deleted.