Pin protobuf version
Pin protobuf version

Older versions of pip miscalculate the protobuf version to install when
given >=3.0.0a2 as minimal dependency installing 3.0.0-alpha-1 instead.
The older version does not have the syntax field in the class
constructor causing a crash.

Resolves #10

QuLogic/ocropy,QuLogic/ocropy,mittagessen/kraken,mittagessen/kraken,mittagessen/kraken,mittagessen/kraken