Update codecov badge

Author: bflammers

README.md

@@ -4,7 +4,7 @@
 [![CRAN\_Status\_Badge](http://www.r-pkg.org/badges/version/ANN2)](https://cran.r-project.org/package=ANN2) 
 ![Monthly downloads](https://cranlogs.r-pkg.org/badges/ANN2)
 ![R CMD check](https://github.com/bflammers/ANN2/workflows/R-CMD-check/badge.svg)
-[![codecov](https://app.codecov.io/gh/bflammers/ANN2/branch/dev/graph/badge.svg)](https://app.codecov.io/gh/bflammers/ANN2)
+[![codecov](https://codecov.io/gh/bflammers/ANN2/graph/badge.svg?token=gwKZcUN4Az)](https://codecov.io/gh/bflammers/ANN2)
 
 Artificial Neural Networks package for R