Add wc-i18n v2 support

This allows users of wc-i18n#2.0.0 (or greater) to inline locales using gulp-wc-i18n.

This functionality is opt in only, to do so, pass a config object with the version prop set to 2 to gulp-wc-i18n

Example

var gulp = require('gulp');
var wcI18n = require('gulp-wc-i18n');

gulp.task('webcomponent:i18n', function() {
  return gulp.src('**/*.html')
    .pipe(wcI18n({
      version: 2
    }))
    .pipe(gulp.dest('./dist'));
});