case sensitive path for ipynb/Jotto.ipynb and ipynb/jotto.ipynb

[bmerkle]

there is a problem when checking out on windows because Jotto.ipynb is also used in lower cases only.

Problem: git clone ....

warning: the following paths have collided (e.g. case-sensitive paths on a case-insensitive filesystem) and only one from the same colliding group is in the working tree:

'ipynb/Jotto.ipynb' 'ipynb/jotto.ipynb'