Running tests now creates a diff due to saved capacity scaling demo

[danielolsen]

When submitting/merging #184, I didn't update the changes to files in powersimdata/design/demo/data/save_files because I didn't think they mattered. But now whenever we run tests, these files are modified again and so now they create a diff from HEAD, precluding the use of helpful shortcuts like git add -u and requiring git reset HEAD --hard to rebase, change branches, etc.

Potential solutions:

• Commit a change to these files
• Modify .gitignore to ignore this folder
• Have the tests clean up after themselves and delete the created files (then commit the deletion so that's not a diff)

[dmuldrew]

I suppose the .gitignore solution is probably the least work

[rouille]

I noticed that the files were changed after running the tests. As @dmuldrew said, ignoring the folder via the .gitignore is the least work.