Merge branch '0.5.4' into 0.6.0

Author: wkh237

src/android/src/main/java/com/RNFetchBlob/RNFetchBlobReq.java

@@ -1,9 +1,5 @@
 package com.RNFetchBlob;
 
-import android.app.DownloadManager;
-import android.content.Context;
-import android.net.Uri;
-
 import com.facebook.react.bridge.Callback;
 import com.facebook.react.bridge.ReactApplicationContext;
 import com.facebook.react.bridge.ReadableArray;
@@ -102,6 +98,8 @@ public void run() {
 
         try {
 
+            req = new AsyncHttpClient();
+
             // use trusty SSL socket
             if(this.options.trusty) {
                 KeyStore trustStore = KeyStore.getInstance(KeyStore.getDefaultType());