chore(system.config.js): remove slash in front of "bundle"

closes #1961
This slash before the bundles path is generating a double slash for the scripts path, e.g. http://localhost:3000/node_modules/@angular/common//bundles/common.umd.js. Some server are not happy with this double slash and redirect to 404 pages like Firebase Hosting.

Author: ziglee

public/docs/_examples/quickstart/ts/systemjs.config.1.js

@@ -41,7 +41,7 @@
 
   // Bundled (~40 requests):
   function packUmd(pkgName) {
-    packages['@angular/'+pkgName] = { main: '/bundles/' + pkgName + '.umd.js', defaultExtension: 'js' };
+    packages['@angular/'+pkgName] = { main: 'bundles/' + pkgName + '.umd.js', defaultExtension: 'js' };
   }
 
   // Most environments should use UMD; some (Karma) need the individual index files

public/docs/_examples/systemjs.config.js

@@ -40,7 +40,7 @@
 
   // Bundled (~40 requests):
   function packUmd(pkgName) {
-    packages['@angular/'+pkgName] = { main: '/bundles/' + pkgName + '.umd.js', defaultExtension: 'js' };
+    packages['@angular/'+pkgName] = { main: 'bundles/' + pkgName + '.umd.js', defaultExtension: 'js' };
   }
 
   // Most environments should use UMD; some (Karma) need the individual index files