Update publishing section

[cderv]

We should remove travis part following https://twitter.com/peter_szilagyi/status/1437646118700175360

Section is: https://bookdown.org/yihui/blogdown/travis-github.html

[swcyo]

We should remove travis part following https://twitter.com/peter_szilagyi/status/1437646118700175360

Section is: https://bookdown.org/yihui/blogdown/travis-github.html

Since June 15th, 2021, the building on travis-ci.org is ceased. Please use travis-ci.com from now on.