Update swift version to 4.1 for Xcode 9.3.

After upgrading to Xcode 9.3, I get the following error:
dyld: Library not loaded: @rpath/libswiftCore.dylib
  Referenced from: /Users/chris/Library/Developer/CoreSimulator/Devices/.../data/Containers/Bundle/Application/.../RE-vibe.app/Frameworks/Zip.framework/Zip
  Reason: image not found

I have tried several different approaches, but none have fixed the issue. I suspect the the swift version for this package needs to be upgraded to match Xcode 9.3's version.

.swift-version

-4.0
+4.1