Test coverage using github workflow

With the current travis configuration, installation of covr failed,
presumably because of the use of the Xenial distribution which is
rather outdated meanwhile. The error occurred when installation of
curl was attempted on travis:

Error: C++17 standard requested but CXX17 is not defined

1 files changed, 1 insertions, 1 deletions

diff --git a/README.md b/README.md
index fcb931f..758952d 100644
--- a/README.md
+++ b/README.md
@@ -8,7 +8,7 @@
 [![](https://www.r-pkg.org/badges/version/chemCal)](https://cran.r-project.org/package=chemCal)
 [![Build
 Status](https://app.travis-ci.com/jranke/chemCal.svg?token=Sq9VuYWyRz2FbBLxu6DK&branch=main)](https://app.travis-ci.com/jranke/chemCal)
-[![codecov](https://codecov.io/github/jranke/chemCal/branch/master/graphs/badge.svg)](https://codecov.io/github/jranke/chemCal)
+[![Codecov test coverage](https://codecov.io/gh/jranke/chemCal/graph/badge.svg)](https://app.codecov.io/gh/jranke/chemCal)
 <!-- badges: end -->
 
 ## Overview