Fails on %USERPROFILE% whitespace

Having a whitespace in _USERPROFILE=C:\Users\Nicolas Le Gland_ made _keybase-installer.cmd_ fail like it's 1995 again:

```
error: exit code 2
warn: gpg: can't create `C:\Users\Nicolas.lock':
warn: gpg: keyblock resource `C:\Users\Nicolas': general error
warn: gpg: error reading key: public key not found
```

I worked the issue around with some _set USERPROFILE=**C:\Users\NICOLA~1**_ voodoo for the current shell, but I wish it was more robust in the first place.

Once installed, I have to rely on this magic to run _keybase.cmd_ too.

Start by inspecting keybase-installer.cmd and keybase.cmd, then reproduce the failure with USERPROFILE set to a Windows path containing whitespace. Trace how the path is passed to GPG and verify that installation and subsequent keybase.cmd execution work without the short-path workaround.

Written by the indexing model from the issue text.