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.

tools/broccoli/trees/node_tree.ts

@@ -30,6 +30,7 @@ module.exports = function makeNodeTree(destinationPath) {
   var typescriptTree = compileWithTypescript(modulesTree, {
     allowNonTsExtensions: false,
     emitDecoratorMetadata: true,
+    experimentalDecorators: true,
     declaration: true,
     mapRoot: '', /* force sourcemaps to use relative path */
     module: 'commonjs',