Use lowercase directories to fix test

[jwilner]

#1226 appears to have introduced a test failure into master via a combination of factors.

My current theory:

1. A test refers to a test data directory in camel-case, but the directory isn't actually camel-case
2. This camel-case test passed locally for me because MacOS's fs is case-insensitive
3. This test somehow did not run on the PR build
4. It finally ran against master where the fs was not case-insensitive

Success in PR -- TestPathPrefix is nowhere present

Failure in master

[jwilner]

Passing now in latest run:

[jwilner]

The erroneously passing PR build above seems to not be building the correct commit.

It says it's checking out the commit c0121d51:

commit 83277cb66eb0f68ec40b336ee55ee9c626970e13
Date:   Thu Jul 9 23:49:10 2020 -0500

    Merge c0121d51bfcb007eae86fac87fba5ea3b6bf2f26 into 916213c5968d710e9f00407feb58024105ce6457

But it's supposed to be building on 2dca06e -- the next commit... I'm disturbed.

[SVilgelm]

Looks good to me. Thank you

[SVilgelm]

I'm merging to unblock the CI