Fixes duplicate comments in minified JS build

Prior to this fix we saw repeated comments in the build for minified
JS. Whilst this is otherwise fine for the unminified build (at this
time) we shouldn’t be including dupes for license headers.

gulpfile.js

@@ -217,11 +217,13 @@ gulp.task('scripts', function () {
     .pipe($.sourcemaps.init())
     // Concatenate Scripts
     .pipe($.concat('material.js'))
-    .pipe($.header(banner, {pkg: pkg}))
     .pipe(gulp.dest('./dist'))
     // Minify Scripts
-    .pipe($.uglify({preserveComments: 'some', sourceRoot: '.',
-        sourceMapIncludeSources: true}))
+    .pipe($.uglify({
+      sourceRoot: '.',
+      sourceMapIncludeSources: true
+    }))
+    .pipe($.header(banner, {pkg: pkg}))
     .pipe($.concat('material.min.js'))
     // Write Source Maps
     .pipe($.sourcemaps.write('./'))