Trim trailing whitespace in config file

[jacob-horton]

I noticed one of the options in my config file wasn't working. It turned out this is because it had a space at the end of the line

I thought it could be nice to trim the whitespace at the end of the line so we don't leave people head scratching like I was! If preferred, we could spit out a warning instead of trimming. Then that would make it easier to find out why a configuration isn't working

I don't often write C, so feel free to suggest any changes, I'll be happy to implement them!

Also, I'm new to this repo, so if there's already something like trim_end I should be using instead, or if I should move the function to another file, please let me know 🙂