Avoid panicking on CLI error

[blast-hardcheese]

This isn't great:

$ upm init
Error: unknown command "init" for "upm"

Did you mean this?
        info

Run 'upm --help' for usage.
panic: unknown command "init" for "upm"

Did you mean this?
        info


goroutine 1 [running]:
github.com/replit/upm/internal/cli.DoCLI()
        .../upm/internal/cli/cli.go:344 +0x1888
main.main()
        .../upm/cmd/upm/main.go:10 +0x1c

Since cobra already does its own error logging, we can probably just exit 1 and call it a day.

[masad-frost]

Oof, thanks.