unable to build with heka 0.10.0

[prfalken]

adding heka-prometheus plugin to heka cmake ends up with :

CMake Error at cmake/ExternalProject.cmake:1522 (add_custom_target):
  add_custom_target cannot create target "protobuf" because another target
  with the same name already exists.  The existing target is a custom target
  created in source directory "/heka".  See documentation for policy CMP0002
  for more details.
Call Stack (most recent call first):
  cmake/externals.cmake:50 (externalproject_add)
  cmake/plugin_loader.cmake:6 (git_clone)
  cmake/externals.cmake:181 (include)
  CMakeLists.txt:105 (include)