Fix protoc arguments. (#102)
Fix protoc arguments. (#102)

protoc commandline invocation fails when protoCompilerArgs is
empty (i.e. prevent adding an empty string '' as a parameter).

Fixes #101.
googleapis/packman,geigerj/packman,googleapis/packman,geigerj/packman,googleapis/packman,geigerj/packman,geigerj/packman,googleapis/packman