Fix require path in test

[Legogris]

npm run dev fails on current master due to invalid casing in filename. This fixes that.

[coveralls]

Coverage remained the same at 76.517% when pulling 9be7b90 on Legogris:fix/requiretestpath into 12b2d2b on gregnb:master.

[gabrielliwerant]

Hm, I don't experience this issue. Can you provide details of your setup like version for npm, node, operating system, etc., so that I might gain some insight?

[Legogris]

I don't suppose you're on Windows @gregnb (paths are case-insensitive on Windows but not on Linux/OS X)? There is no Cities.json or Cities.js in the folder.

[patorjk]

I can verify this, it doesn't work on codesandbox: https://codesandbox.io/s/github/gregnb/mui-datatables

I also added a fix as part of this PR: #1087

Edit: Actually, I just tried again, and it currently works fine on Mac OS X (which is what I use). It was only on codesandbox where I noticed the issue (I was getting ready to put in the PR and include a link to codesandbox and it didn't work so I fixed the typo before submitting).

[gabrielliwerant]

I don't see the problem on Windows, but I don't see any harm in changing it to lowercase, as that is how it is used elsewhere, and that is the exact filename, so it should be fixed. Thanks for pointing this out @Legogris and thanks for helping to verify @patorjk.

[Legogris]

I don't see the problem on Windows, but I don't see any harm in changing it to lowercase, as that is how it is used elsewhere, and that is the exact filename, so it should be fixed. Thanks for pointing this out @Legogris and thanks for helping to verify @patorjk.

FYI for the future, apart from Windows on NTFS/FAT, paths are generally case-sensitive on all filesystems and OS's in mainstream use today.

It's expected that Windows doesn't care about casing; Linux/BSD/OS X does.

[gabrielliwerant]

Closes #1157.