Fix drive letter case sensitivity

[Herschel]

On Windows, a lowercase drive letter would cause hmm reinstall to vomit:

c:\projects\funkin>hmm reinstall
Execution error: failed to extract expected "haxelib path discord_rpc" information (path, name, and version) for library: discord_rpc
Use "hmm help" to see usage

c:\projects\funkin>cd C:\projects\funkin

C:\projects\funkin>hmm reinstall
git library "discord_rpc" (url: https://github.com/Aidan63/linc_discord-rpc, ref: 2d83fa863ef0c1eace5f1cf67c3ac315d1a3a8a5, dir: N/A) already installed
git library "flixel" (url: https://github.com/FunkinCrew/flixel, ref: 5823c46b4e7410372d58b99f8d5c52fc18b3cb3d, dir: N/A) already installed
...

Change pathRegex to allow for lowercase drive letters.