Use more ES2015.

_baseIsNative.js

@@ -7,23 +7,23 @@ import toSource from './_toSource.js';
  * Used to match `RegExp`
  * [syntax characters](http://ecma-international.org/ecma-262/7.0/#sec-patterns).
  */
-var reRegExpChar = /[\\^$.*+?()[\]{}|]/g;
+const reRegExpChar = /[\\^$.*+?()[\]{}|]/g;
 
 /** Used to detect host constructors (Safari). */
-var reIsHostCtor = /^\[object .+?Constructor\]$/;
+const reIsHostCtor = /^\[object .+?Constructor\]$/;
 
 /** Used for built-in method references. */
-var funcProto = Function.prototype,
-    objectProto = Object.prototype;
+const funcProto = Function.prototype;
+const objectProto = Object.prototype;
 
 /** Used to resolve the decompiled source of functions. */
-var funcToString = funcProto.toString;
+const funcToString = funcProto.toString;
 
 /** Used to check objects for own properties. */
-var hasOwnProperty = objectProto.hasOwnProperty;
+const hasOwnProperty = objectProto.hasOwnProperty;
 
 /** Used to detect if a method is native. */
-var reIsNative = RegExp('^' +
+const reIsNative = RegExp('^' +
   funcToString.call(hasOwnProperty).replace(reRegExpChar, '\\$&')
   .replace(/hasOwnProperty|(function).*?(?=\\\()| for .+?(?=\\\])/g, '$1.*?') + '$'
 );
@@ -40,7 +40,7 @@ function baseIsNative(value) {
   if (!isObject(value) || isMasked(value)) {
     return false;
   }
-  var pattern = isFunction(value) ? reIsNative : reIsHostCtor;
+  const pattern = isFunction(value) ? reIsNative : reIsHostCtor;
   return pattern.test(toSource(value));
 }