Update Prettier to version 2.0

Please note that these changes were done automatically, using `gulp lint --fix`.

Given that the major version number was increased, there's a fair number of (primarily whitespace) changes; please see https://prettier.io/blog/2020/03/21/2.0.0.html
In order to reduce the size of these changes somewhat, this patch maintains the old "arrowParens" style for now (once mozilla-central updates Prettier we can simply choose the same formatting, assuming it will differ here).

web/text_layer_builder.js

@@ -111,7 +111,7 @@ class TextLayerBuilder {
         this._finishRendering();
         this._updateMatches();
       },
-      function(reason) {
+      function (reason) {
         // Cancelled or failed to render text layer; skipping errors.
       }
     );