Replace lodash/assign with Object.assign (#5356)

Remove imports to lodash/assign and replace assign with Object.assign.
The lodash/assign is unnecessary for babel 7 as node >4 has the same
functionality built-in with Object.assign as used here.

This resolve the [issue 5353](https://github.com/babel/babel/issues/5353)

packages/babel-core/src/transformation/plugin.js

@@ -2,7 +2,6 @@ import OptionManager from "./file/options/option-manager";
 import * as messages from "babel-messages";
 import Store from "../store";
 import traverse from "babel-traverse";
-import assign from "lodash/assign";
 import clone from "lodash/clone";
 
 const GLOBAL_VISITOR_PROPS = ["enter", "exit"];
@@ -12,7 +11,7 @@ export default class Plugin extends Store {
     super();
 
     this.initialized = false;
-    this.raw         = assign({}, plugin);
+    this.raw         = Object.assign({}, plugin);
     this.key         = this.take("name") || key;
 
     this.manipulateOptions = this.take("manipulateOptions");

packages/babel-template/src/index.js

@@ -1,5 +1,4 @@
 import cloneDeep from "lodash/cloneDeep";
-import assign from "lodash/assign";
 import has from "lodash/has";
 import traverse from "babel-traverse";
 import * as babylon from "babylon";
@@ -23,7 +22,7 @@ export default function (code: string, opts?: Object): Function {
     }
   }
 
-  opts = assign({
+  opts = Object.assign({
     allowReturnOutsideFunction: true,
     allowSuperOutsideMethod: true,
     preserveComments: false,

packages/babel-traverse/src/path/index.js

@@ -4,7 +4,6 @@ import * as virtualTypes from "./lib/virtual-types";
 import buildDebug from "debug";
 import invariant from "invariant";
 import traverse from "../index";
-import assign from "lodash/assign";
 import Scope from "../scope";
 import * as t from "babel-types";
 import { path as pathCache } from "../cache";
@@ -164,7 +163,7 @@ export default class NodePath {
   }
 }
 
-assign(NodePath.prototype,
+Object.assign(NodePath.prototype,
   NodePath_ancestry,
   NodePath_inference,
   NodePath_replacement,