lib Types and Documentations Fix

src/harness/fourslashInterfaceImpl.ts

@@ -1168,6 +1168,7 @@ namespace FourSlashInterface {
             typeEntry("Partial"),
             typeEntry("Required"),
             typeEntry("Readonly"),
+            typeEntry("Writable"),
             typeEntry("Pick"),
             typeEntry("Record"),
             typeEntry("Exclude"),

src/lib/es2015.collection.d.ts

@@ -30,7 +30,7 @@ interface WeakMap<K extends object, V> {
 }
 
 interface WeakMapConstructor {
-    new <K extends object = object, V = any>(entries?: readonly [K, V][] | null): WeakMap<K, V>;
+    new <K extends object = object, V = any>(entries?: readonly (readonly [K, V])[] | null): WeakMap<K, V>;
     readonly prototype: WeakMap<object, any>;
 }
 declare var WeakMap: WeakMapConstructor;