Update remote theme version to 6.0.0

Author: bedroesb

_config.yml

@@ -7,7 +7,7 @@ topnav_title: Website title
 description: "Example of ELIXIR toolkit theme as a remote jekyll theme"
 # Metadata description of the website
 
-remote_theme: ELIXIR-Belgium/elixir-toolkit-theme@latest
+remote_theme: ELIXIR-Belgium/elixir-toolkit-theme@6.0.0
 
 exclude:
   - README.md