Black has syntax error with valid iPython magic when using --pipe

To reproduce:

This occurs on black, version 19.10b0 and ‘jupytext==1.5.2’. When --sync a notebook to py:percent format using the following command:

jupytext --update-metadata '{"jupytext":{"notebook_metadata_filter":"all", "cell_metadata_filter":"-all"}, "accelerator":"GPU"}' --set-formats 'nb_python//py:percent,colabs//ipynb' --pipe black --pipe "sed s/[[:space:]]*\#[[:space:]]\%\%/\#\%\%/g"  --pipe 'isort -' --pipe-fmt 'py:percent' --sync

I get this error:

executing black -
error: cannot format -: Cannot parse: 73:0: !~/miniconda.sh -b -p $HOME/miniconda

Now I tracked down the error, and when I change the lines ipynb to use !bash ~/miniconda.sh -b -p $HOME/miniconda, it works just fine. Also the following lines also generated error:

error: cannot format -: Cannot parse: 78:0: !. activate habitat;``` 

I had to change it to
```bash
!conda . activate

I also had to change:

!./test_locally_pointnav_rgbd.sh

to

!bash ./test_locally_pointnav_rgbd.sh

TLDR: Black has issues when the first arg following ‘!’ isn’t a command, but references an executable file or another bash alias.

[Skylion007]

@mwouts I opened a PR that solves the issue.

[mwouts]

Thanks @Skylion007 for the fix. And for the notebook examples. Great project by the way!