Bump to v4.16.5.

isString.js

@@ -1,19 +1,10 @@
+import baseGetTag from './_baseGetTag.js';
 import isArray from './isArray.js';
 import isObjectLike from './isObjectLike.js';
 
 /** `Object#toString` result references. */
 var stringTag = '[object String]';
 
-/** Used for built-in method references. */
-var objectProto = Object.prototype;
-
-/**
- * Used to resolve the
- * [`toStringTag`](http://ecma-international.org/ecma-262/7.0/#sec-object.prototype.tostring)
- * of values.
- */
-var objectToString = objectProto.toString;
-
 /**
  * Checks if `value` is classified as a `String` primitive or object.
  *
@@ -33,7 +24,7 @@ var objectToString = objectProto.toString;
  */
 function isString(value) {
   return typeof value == 'string' ||
-    (!isArray(value) && isObjectLike(value) && objectToString.call(value) == stringTag);
+    (!isArray(value) && isObjectLike(value) && baseGetTag(value) == stringTag);
 }
 
 export default isString;