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).

src/core/annotation.js

@@ -503,7 +503,7 @@ class Annotation {
       }
 
       const objectLoader = new ObjectLoader(resources, keys, resources.xref);
-      return objectLoader.load().then(function() {
+      return objectLoader.load().then(function () {
         return resources;
       });
     });
@@ -941,7 +941,7 @@ class TextWidgetAnnotation extends WidgetAnnotation {
         resources: this.fieldResources,
         operatorList,
       })
-      .then(function() {
+      .then(function () {
         return operatorList;
       });
   }