fix gpt-2 unk token test

docs/README.md

@@ -57,4 +57,4 @@ It should build the static app that will be available under `/docs/_build/html`
 ## Adding a new element to the tree (toc-tree)
 
 Accepted files are reStructuredText (.rst) and Markdown (.md). Create a file with its extension and put it
-in the source directory. You can then link it to the toc-tree by putting the filename without the extension.
+in the source directory. You can then link it to the toc-tree by putting the filename without the extension.