Update .travis.yml

stop using dev version of remotes package

.travis.yml

@@ -3,7 +3,6 @@ r: bioc-devel
 sudo: false
 cache: packages
 warnings_are_errors: false
-before_install: R -e 'source("https://install-github.me/r-lib/remotes")'
 after_success:
     - Rscript -e 'covr::codecov()'
 addons: