Merge pull request #10818 from falsandtru/lib.d.ts/map

Fix {Map,WeakMap}.prototype.set method signatures (#10694)

Author: mhegazy

lib/lib.es2015.collection.d.ts

@@ -20,7 +20,7 @@ interface Map<K, V> {
     forEach(callbackfn: (value: V, index: K, map: Map<K, V>) => void, thisArg?: any): void;
     get(key: K): V | undefined;
     has(key: K): boolean;
-    set(key: K, value?: V): this;
+    set(key: K, value: V): this;
     readonly size: number;
 }
 
@@ -36,7 +36,7 @@ interface WeakMap<K, V> {
     delete(key: K): boolean;
     get(key: K): V | undefined;
     has(key: K): boolean;
-    set(key: K, value?: V): this;
+    set(key: K, value: V): this;
 }
 
 interface WeakMapConstructor {