link to 'exercises' in '/notebooks/README.md' doesn't work

For some reason 'exercises' -link (https://github.com/csc-training/python-introduction/blob/gh-pages/notebooks/exersises) doesn't work.
I think it should redirect to 'https://github.com/csc-training/python-introduction/tree/gh-pages/notebooks/exercises'. 
'examples' and 'answers' -links that redirect to '.../tree/gh-pages/notebooks/examples' and .../tree/gh-pages/notebooks/answers' work fine.