Server Side Fork Unable to Create Folders

Hi, can't to get the server side fork to work, I'm pretty sure it's trying to create the folder with colons in the name. However Windows doesn't allow colons in folder names. The dimension being saved as minecraft:overworld instead of just overworld like in the stable branch.

See error starting on line 676
https://mclo.gs/r0WDKw6

mclo.gs