Have travis build with model test enabled

Author: Sandro Santilli

.travis.yml

@@ -18,7 +18,8 @@ before_install:
 install:
   - mkdir build
   - cd build
-  - cmake -DWITH_SERVER=ON -DWITH_STAGED_PLUGINS=OFF -DWITH_GRASS=OFF -DSUPPRESS_QT_WARNINGS=ON ..
+  - cmake -DWITH_SERVER=ON -DWITH_STAGED_PLUGINS=OFF -DWITH_GRASS=OFF \
+          -DSUPPRESS_QT_WARNINGS=ON -DENABLE_MODELTEST=ON ..
 
 script: xvfb-run ctest -V -E 'Atlas|atlas|PyQgsPalLabelingCanvas|PyQgsPalLabelingServer|qgis_wcsprovidertest' -S ../qgis-test-travis.ctest --output-on-failure