Fix deploy script (#176)

Use posix style function instead of bash style.

.travis/deploy_dockerhub.sh

@@ -1,6 +1,6 @@
-#!/bin/sh
+#!/bin/bash
 
-function deploy {
+deploy () {
 		docker login -e $DOCKER_EMAIL -u $DOCKER_USER -p $DOCKER_PASS
 		docker push maxking/mailman-web:$1
 		docker push maxking/mailman-core:$1