Stack: build is broken because of version mismatch

[Riscky]

In #105 we changed our builds from local builds with Stack to CI builds with Nix.
Because of the package versions found in nixpkgs we updated the version of the base16-bytestring dependency to >= 1.0
This caused a few lines of code to change:

hoff/src/Server.hs

Lines 66 to 69 in e1c0c13

	in case binaryDigest of
	-- If the hexDigest was not hexadecimal, is was definitely not valid
	Left _ -> False
	Right x -> case digestFromByteString x of

due to a changed function type in the base16-bytestring package.

Because of this change, Hoff does not build with Stack.
We need to pin a newer version of base16-bytestring, which is in newer Stack LTS versions, but this breaks the github dependency, an updated version of which is only found in very new Stack LTS versions.