fix(core.umd.js): ship ES5 compatible UMD file

The UMD file was not ES5 compatible.

Fixes #783

BREAKING CHANGE:
The files under `/esm` are ES5 (before: ES2015) based with ES2015 modules.
In the real world, this should not cause troubles.

assets/release/README.md

@@ -6,7 +6,7 @@ The sources for this package are in the [angular2-google-maps](https://github.co
 This package contains different sources for different users:
 
 1. The files located in the root dir are ES5 compatible files that can be consumed using CommonJS.
-2. The files under `/esm` are ES6 compatible files that can be transpiled to E5 using any transpiler.
+2. The files under `/esm` are ES5 based with ES2015 modules.
 3. The files under `/ts` are the TypeScript source files.
 4. Files with the name pattern *.umd.js are UMD bundled modules for fast load times during development.
 

tsconfig.es2015.json

@@ -1,7 +1,7 @@
 {
     "compilerOptions": {
         "module": "es2015",
-        "target": "es2015",
+        "target": "es5",
         "noImplicitAny": true,
         "experimentalDecorators": true,
         "emitDecoratorMetadata": true,