fix Pool type

Author: jmordica

typings/mysql/index.d.ts

@@ -14,7 +14,7 @@ import Server = require('./lib/Server');
 
 export function createConnection(connectionUri: string): Connection;
 export function createConnection(config: BaseConnection.ConnectionOptions): Connection;
-export function createPool(config: BasePool.PoolOptions): Pool;
+export function createPool(config: BasePool.PoolOptions): BasePool;
 export function createPoolCluster(config?: BasePoolCluster.PoolClusterOptions): PoolCluster;
 export function escape(value: any): string;
 export function escapeId(value: any): string;

typings/mysql/lib/Pool.d.ts

@@ -60,6 +60,8 @@ declare class Pool extends EventEmitter {
 
     on(event: string, listener: Function): this;
     on(event: 'connection', listener: (connection: PoolConnection) => any): this;
+
+    promise(promiseImpl?: any): any
 }
 
 export = Pool;