choosenim binary builds for macOS need 10.13
So I just got this error after upgrading:

```
~ » choosenim update devel
   Updating devel
Downloading Nim devel from GitHub
[##################################################] 100.0% 0kb/s
 Extracting nim-1.1.1-osx.tar.xz
dyld: lazy symbol binding failed: Symbol not found: _futimens
  Referenced from: /Users/dom/.nimble/bin/choosenim (which was built for Mac OS X 10.13)
  Expected in: /usr/lib/libSystem.B.dylib

dyld: Symbol not found: _futimens
  Referenced from: /Users/dom/.nimble/bin/choosenim (which was built for Mac OS X 10.13)
  Expected in: /usr/lib/libSystem.B.dylib

[1]    34238 trace trap  choosenim update devel
```

@genotrance any way we can fix that in the CI? I guess I will rebuild choosenim on my machine manually and upload the release there so that it's more compatible with older macOS versions.