migrate away from travis

[sahirbhatnagar]

As outlined in this post it is recommended to mirate away from travis in favor of github actions.

As outlined here, it's as simple as removing the _travis.yml file and de-activating the repo on travis. Follow this by a call to usethis::use_github_action_check_standard() to mimic R CMD CHECK and usethis::use_pkgdown_github_pages() for building and pushing the pkgdown website to gh-pages branch