Incompatible with Adafruit Huzzah ESP8266 board

[jtwalters]

There was a regression that broke building for the Huzzah ESP8266 board, around commit 2e2a87d

FireThing.cpp 'D1' was not declared in this scope

If you have this board, checkout the repo and then cherry-pick the fingerprint commit:

git checkout 7226a6b7dd9dbb5ea7c08c3b2d86f1d104b91fad
git cherry-pick 058744e21184e84c791536e296c57a6ca1e40373

Then it will compile successfully.

[proppy]

weird that travis didn't catch this. We should split the firethings/modem project from the rest of the library to avoid having them bleed on each other.