Make ci_integration.sh use bash

The ci_integration.sh script uses double brackets ('[[') test
which is not portable. For instance, running it with dash you
get the error:

./ci/ci_integration.sh: 10: ./ci/ci_integration.sh: [[: not found

This change makes the script use bash, that supports this kind
of test.

Fixes #6939

ci/ci_integration.sh

@@ -1,4 +1,4 @@
-#!/bin/sh
+#!/usr/bin/env bash
 set -e
 
 # Since we are using the system jruby, we need to make sure our jvm process