kbstage: gpg not found in $PATH

I'm trying the new kbstage. It's not detecting gpg in my $PATH.

```
ugh ~ kbstage login
▶ WARNING Running in staging mode
keybase passphrase:
Enter a public name for this device: ugh
How would you like to sign this install of Keybase?

(1) using PGP (requires access to your PGP key)
(999) Cancel, I'll login later (cancel)
Choose a signing option: 1
▶ INFO deviceSignPGP error: exec: "gpg": executable file not found in $PATH
How would you like to sign this install of Keybase?

(1) using PGP (requires access to your PGP key)
(999) Cancel, I'll login later (cancel)
Choose a signing option: 999
▶ ERROR cancel requested by user
ugh ~ which gpg
/usr/local/bin/gpg
ugh ~ echo $PATH
/Users/peter/bin /usr/local/go/bin /usr/local/bin /usr/bin /bin /usr/local/sbin /usr/sbin /sbin
ugh ~
```

Start by reproducing the issue with `kbstage login`, then compare `which gpg` and the displayed `$PATH` from the report. Trace the kbstage signing flow for the PGP option and determine why it cannot find `/usr/local/bin/gpg`; done means the reported environment detects gpg and the login flow proceeds past PGP selection.

Written by the indexing model from the issue text.