fix: from now _acquire return always a promise to avoid uncatchable exception

Author: bombjackit

lib/base/connection-pool.js

@@ -363,7 +363,7 @@ class ConnectionPool extends EventEmitter {
    */
 
   acquire (requester, callback) {
-    const acquirePromise = shared.Promise.resolve(this._acquire().promise).catch(err => {
+    const acquirePromise = shared.Promise.resolve(this._acquire()).catch(err => {
       this.emit('error', err)
       throw err
     })
@@ -382,7 +382,7 @@ class ConnectionPool extends EventEmitter {
       return shared.Promise.reject(new ConnectionError('Connection is closing', 'ENOTOPEN'))
     }
 
-    return this.pool.acquire()
+    return this.pool.acquire().promise
   }
 
   /**