Updated the style of the examples

* const/let instead of var
* classes
* pass our own eslint checks

lib/jasmine-core/example/src/Song.js

@@ -1,7 +1,6 @@
-function Song() {
+class Song {
+  persistFavoriteStatus(value) {
+    // something complicated
+    throw new Error('not yet implemented');
+  }
 }
-
-Song.prototype.persistFavoriteStatus = function(value) {
-  // something complicated
-  throw new Error("not yet implemented");
-};