test(@angular/cli): output test compilation to es5

Fixes angular#5185

Author: Brocco

packages/@angular/cli/blueprints/ng/files/__path__/tsconfig.spec.json

@@ -12,7 +12,7 @@
     ],<% } %>
     "outDir": "<%= relativeRootPath %>/out-tsc/spec",
     "module": "commonjs",
-    "target": "es6",
+    "target": "es5",
     "baseUrl": "",
     "types": [
       "jasmine",