Fix IDBIndex interface for openCursor/openKeyCursor

**TypeScript Version:** 

master

**Expected:**

https://www.w3.org/TR/IndexedDB/

``` ts
    openCursor(range?: any, direction?: string): IDBRequest;
    openKeyCursor(range?: any, direction?: string): IDBRequest;
```

**Actual:** 

``` ts
    openCursor(range?: IDBKeyRange, direction?: string): IDBRequest;
    openKeyCursor(range?: IDBKeyRange, direction?: string): IDBRequest;
```
