fix(common): Fix signature of for objects (make target optional)

src/common/common.ts

@@ -295,7 +295,7 @@ export function find(collection: any, callback: any) {
 export let mapObj: <T, U>(collection: { [key: string]: T }, callback: Mapper<T, U>, target?: typeof collection) => { [key: string]: U } = map;
 /** Given an array, returns a new array, where each element is transformed by the callback function */
 export function map<T, U>(collection: T[], callback: Mapper<T, U>, target?: typeof collection): U[];
-export function map<T, U>(collection: { [key: string]: T }, callback: Mapper<T, U>, target: typeof collection): { [key: string]: U };
+export function map<T, U>(collection: { [key: string]: T }, callback: Mapper<T, U>, target?: typeof collection): { [key: string]: U };
 /** Maps an array or object properties using a callback function */
 export function map(collection: any, callback: any, target: typeof collection): any {
   target = target || (isArray(collection) ? [] : {});