[fix] ES5 Object.keys only accepts an object

Author: ljharb

src/lib/es2015.core.d.ts

@@ -298,6 +298,12 @@ interface ObjectConstructor {
      */
     getOwnPropertySymbols(o: any): symbol[];
 
+    /**
+      * Returns the names of the enumerable properties and methods of an object.
+      * @param o Object that contains the properties and methods. This can be an object that you created or an existing Document Object Model (DOM) object.
+      */
+    keys(o: {}): string[];
+
     /**
      * Returns true if the values are the same value, false otherwise.
      * @param value1 The first value.

src/lib/es5.d.ts

@@ -238,7 +238,7 @@ interface ObjectConstructor {
       * Returns the names of the enumerable properties and methods of an object.
       * @param o Object that contains the properties and methods. This can be an object that you created or an existing Document Object Model (DOM) object.
       */
-    keys(o: {}): string[];
+    keys(o: object): string[];
 }
 
 /**