Run deployment under `git tag` command

[weiguoz]

In fact, I followed the instruction ref but failed due to some network problem while running gpg -a --export-secret-keys ...
I left a TODO in .travis.yml.

Error

gpg: no default secret key: secret key not available
gpg: signing failed: secret key not available
[INFO] ------------------------------------------------------------------------
[INFO] BUILD FAILURE
[INFO] ------------------------------------------------------------------------
[INFO] Total time: 24.674 s
[INFO] Finished at: 2019-11-29T13:56:46Z
[INFO] Final Memory: 38M/348M
[INFO] ------------------------------------------------------------------------
[ERROR] Failed to execute goal org.apache.maven.plugins:maven-gpg-plugin:1.6:sign (gpg) on project jsqlflow: Exit code: 2 -> [Help 1]