Removed unused CMake option.

.travis.yml

@@ -6,7 +6,7 @@ branches:
     - master
 before_install:
   - sudo apt-get update; sudo apt-get install qt4-dev-tools libvtk5-dev libvtk5-qt4-dev libnetcdf-dev libshp-dev libgeotiff-dev libboost-dev libboost-date-time-dev libboost-filesystem-dev libboost-program-options-dev libboost-system-dev
-script: "mkdir build && cd build && cmake -DOGS_BUILD_GUI=ON -DOGS_DONT_USE_OPTIONAL_SUBMODULES=ON .. && cmake .. && make && make test"
+script: "mkdir build && cd build && cmake -DOGS_BUILD_GUI=ON .. && cmake .. && make && make test"
 notifications:
   email:
     - lars.bilke@ufz.de