Failed to create relative paths for project file

[ari-party]

[ERROR rojo] Rojo crashed! You are running Rojo 7.7.0-rc.1.
[ERROR rojo] This is probably a Rojo bug.
[ERROR rojo]
[ERROR rojo] Please consider filing an issue: https://github.com/rojo-rbx/rojo/issues
[ERROR rojo]
[ERROR rojo] Details: Failed to create relative paths for project file!: StripPrefixError(())
[ERROR rojo] in file src\cli\sourcemap.rs on line 211

Reproduction:

• Windows machine
• Be on Rojo version 2a1102f or later (cargo install --git https://github.com/rojo-rbx/rojo.git --rev 2a1102fc55a8d8afc1c9f8218d74b7b932ac2a1e)
• Clone rojo-rbx/rojo
• rojo sourcemap plugin.project.json

This issue comes from 2a1102f, and is not present in 02b4113 (previous).
cc @Ivanmatthew