`--force` is required to install firmware for the first time

On my tessel board, `tessel update` failed because there's no firmware installed

```bash
> tessel update
TESSEL! Connected to <SERIAL>.
INFO Checking for latest firmware...
ERR! No builds were found
```

Instead, we should add `--force` option for the first time to install the firmware

```bash
> tessel update -f
TESSEL! Connected to <SERIAL>
INFO Checking for latest firmware...
INFO Downloading firmware from https://builds.tessel.io/firmware/tessel-firmware-current.bin
INFO Updating firmware... please wait. Tessel will reset itself after the update
Waiting for bootloader....
Writing: 100%  1186168 /1186168
Done! 
```