Use gh actions

[olivroy]

Hi @mdancho84,

Could you add gh actions and delete travis.yml?

Locally,

usethis::use_dev_version()
usethis::use_pkgdown_github_pages()
usethis::use_github_action("check-standard")
usethis::use_github_action("test-coverage")
unlink("docs", recursive = TRUE)
unlink(".travis.yml")
use_git_ignore("docs")

Thanks