let the source file format to be xx.ipynb instead of xx.ipynb.txt
let the source file format to be xx.ipynb instead of xx.ipynb.txt

d2l-ai/d2l-zh,mli/gluon-tutorials-zh,mli/gluon-tutorials-zh,d2l-ai/d2l-zh,mli/gluon-tutorials-zh,mli/gluon-tutorials-zh,d2l-ai/d2l-zh