fix(broccoli-typescript): properly parse compilerOptions (#764)

Previously, the settings in tsconfig would be ignored by
the broccoli-typescript plugin, because the whole config's
JSON was being provided to `convertCompilerOptionsFromJson()`
instead of just the expected `compilerOptions`.

lib/broccoli/broccoli-typescript.js

@@ -159,7 +159,7 @@ class BroccoliTypeScriptCompiler extends Plugin {
 
     this._tsConfigFiles = tsconfig.files.splice(0);
 
-    this._tsOpts = ts.convertCompilerOptionsFromJson(tsconfig, '', null).options;
+    this._tsOpts = ts.convertCompilerOptionsFromJson(tsconfig.compilerOptions, '', null).options;
     this._tsOpts.rootDir = '';
     this._tsOpts.outDir = '';