add httpclient pool expired to 3 minutes

Author: chzyer

src/com/qiniu/io/IO.java

@@ -29,7 +29,7 @@ public IO(Client client, String uptoken) {
 	}
 
 	private static Client defaultClient() {
-		if (mClient != null && System.currentTimeMillis() - mClientUseTime > 60 * 1000) { // 1 minute
+		if (mClient != null && System.currentTimeMillis() - mClientUseTime > 3 * 60 * 1000) { // 1 minute
 			mClient.close();
 			mClient = null;
 		}