chore(build): Upgrade to TypeScript@1.5.3

This change also makes us compliant with 1.6.0-dev compiler,
so we can do some experiments with apps that use 1.6 features
and compile against Angular.

We should probably add a travis build for 1.6 so we stay compatible
with both versions.

modules/angular2/test/test_lib/test_lib_spec.ts

@@ -21,7 +21,7 @@ class TestObj {
   someComplexFunc(a) { return a; }
 }
 
-@proxy
+@proxy()
 @IMPLEMENTS(TestObj)
 class SpyTestObj extends SpyObject {
   constructor() { super(TestObj); }