Update .github/CONTRIBUTING.md

Co-Authored-By: sven1103 <[email protected]>

.github/CONTRIBUTING.md

@@ -24,7 +24,7 @@ If you're not used to this workflow with git, you can start with some [basic doc
 
 ## Style guide
 Google provides an excellent [style guide](https://github.com/google/styleguide/blob/gh-pages/pyguide.md), which
-is an best practise extension of [PEP](https://www.python.org/dev/peps/), the Python Enhancement Proposals. Have a look at the
+is a best practise extension of [PEP](https://www.python.org/dev/peps/), the Python Enhancement Proposals. Have a look at the
 [docstring](https://github.com/google/styleguide/blob/gh-pages/pyguide.md#38-comments-and-docstrings) section, which is in particular
 important, as nf-core tool's code documentation is generated out of these automatically.