Fix size() when in chain()

underscore/underscore-tests.ts

@@ -493,10 +493,11 @@ function strong_typed_values_tests() {
         return [r.title, true];
     }).object().value();
 
-    _(dictionaryLike).each((x) => {
+    var x: number = _(dictionaryLike).chain().filter((x) => {
         console.log(x.title);
         console.log(x.value.toFixed());
-    });
+        return x.title == 'item1';
+    }).size().value();
 
     _.values<{title: string, value: number}>(dictionaryLike);
 }

underscore/underscore.d.ts

@@ -2824,7 +2824,7 @@ interface _Chain<T> {
 	* Wrapped type `any`.
 	* @see _.size
 	**/
-	size(): _Chain<T>;
+	size(): _ChainSingle<number>;
 
 	/*********
 	* Arrays *