text: Title: Run Black on master or change flake8 line length
  Body: Working on a fix for #257 as my first contribution to tikzplotlib :) 
  
  As flake8 is set to `max-line-length = 80` for the project, I set `line-length = 80` in Black locally. I understand from one of the commits on #348 that some code on the project is blackified. Although, several files in `/tikzplotlib` are not blackified(?), which makes for a lot of "changed lines" that are only reformatted (on save). I suggest black is run on all the files to make it easier to contribute. 
  
  It might also be the case that the code is indeed blackified at line length 88, in which case the flake8 line length should be changed.