[ci] Use secure for img shields

Author: hazendaz

README.md

@@ -5,7 +5,7 @@ MyBatis Memcached Extension
 [![Coverage Status](https://coveralls.io/repos/mybatis/memcached-cache/badge.svg?branch=master&service=github)](https://coveralls.io/github/mybatis/memcached-cache?branch=master)
 [![Maven central](https://maven-badges.herokuapp.com/maven-central/org.mybatis.caches/mybatis-memcached/badge.svg)](https://maven-badges.herokuapp.com/maven-central/org.mybatis.caches/mybatis-memcached)
 [![Sonatype Nexus (Snapshots)](https://img.shields.io/nexus/s/https/oss.sonatype.org/org.mybatis.caches/mybatis-memcached.svg)](https://oss.sonatype.org/content/repositories/snapshots/org/mybatis/caches/mybatis-memcached/)
-[![License](http://img.shields.io/:license-apache-brightgreen.svg)](http://www.apache.org/licenses/LICENSE-2.0.html)
+[![License](https://img.shields.io/:license-apache-brightgreen.svg)](https://www.apache.org/licenses/LICENSE-2.0.html)
 
 ![mybatis-memcached](http://mybatis.github.io/images/mybatis-logo.png)