adding missing semi-colon to extendsHelper

necessary to avoid linting errors.

src/compiler/transformers/es2015.ts

@@ -4079,7 +4079,7 @@ namespace ts {
                         ({ __proto__: [] } instanceof Array && function (d, b) { d.__proto__ = b; }) ||
                         function (d, b) { for (var p in b) if (b.hasOwnProperty(p)) d[p] = b[p]; };
                     return extendStatics(d, b);
-                }
+                };
 
                 return function (d, b) {
                     extendStatics(d, b);