Use Object Spread Syntax (#7777)

* Use Object Spread Syntax

* Nits

packages/babel-template/src/options.js

@@ -44,7 +44,10 @@ export function merge(a: TemplateOpts, b: TemplateOpts): TemplateOpts {
   } = b;
 
   return {
-    parser: Object.assign({}, a.parser, b.parser),
+    parser: {
+      ...a.parser,
+      ...b.parser,
+    },
     placeholderWhitelist,
     placeholderPattern,
     preserveComments,

packages/babel-template/src/parse.js

@@ -134,14 +134,12 @@ type MetadataState = {
 };
 
 function parseWithCodeFrame(code: string, parserOpts: {}): BabelNodeFile {
-  parserOpts = Object.assign(
-    {
-      allowReturnOutsideFunction: true,
-      allowSuperOutsideMethod: true,
-      sourceType: "module",
-    },
-    parserOpts,
-  );
+  parserOpts = {
+    allowReturnOutsideFunction: true,
+    allowSuperOutsideMethod: true,
+    sourceType: "module",
+    ...parserOpts,
+  };
 
   try {
     return parse(code, parserOpts);