Add missing word to promise constructor explanation

types/es6-shim/index.d.ts

@@ -500,7 +500,7 @@ interface PromiseConstructor {
     /**
      * Creates a new Promise.
      * @param executor A callback used to initialize the promise. This callback is passed two arguments:
-     * a resolve callback used resolve the promise with a value or the result of another promise,
+     * a resolve callback used to resolve the promise with a value or the result of another promise,
      * and a reject callback used to reject the promise with a provided reason or error.
      */
     new <T>(executor: (resolve: (value?: T | PromiseLike<T>) => void, reject: (reason?: any) => void) => void): Promise<T>;