adding apt-get install of the protobuf-compiler
adding apt-get install of the protobuf-compiler

... so that it finds it when building the rock.

(solution found at https://github.com/seishun/SteamPP/commit/71b15130786f006422526638792c43b03bce5ca8 )
bobbens/loadcaffe,hmandal/loadcaffe,fmassa/loadcaffe,uricohen/loadcaffe,szagoruyko/loadcaffe