chore: add an option to specify which tsconfig to use.

Author: hansl

lib/broccoli/angular2-app.js

@@ -272,7 +272,7 @@ class Angular2App extends BroccoliPlugin {
     var sourceTree = this._getSourceTree();
     var configTree = this._getConfigTree();
 
-    var tsConfigPath = path.join(this._sourceDir, 'tsconfig.json');
+    var tsConfigPath = this._options.tsConfig || path.join(this._sourceDir, 'tsconfig.json');
     var tsconfig = JSON.parse(fs.readFileSync(tsConfigPath, 'utf-8'));
 
     // Add all glob files to files. In some cases we don't want to specify