[pom] Use github actions instead of travis ci url
<url>https://github.com/mybatis/jpetstore-6/issues</url>
</issueManagement>
<ciManagement>
- <system>Travis CI</system>
- <url>https://travis-ci.org/mybatis/jpetstore-6</url>
+ <system>GitHub Actions</system>
+ <url>https://github.com/mybatis/jpetstore-6/actions</url>
</ciManagement>
<distributionManagement>
<site>
