[travis] Enable server tests

Author: m-kuhn

.ci/travis/linux/docker-build-test.sh

@@ -49,6 +49,7 @@ cmake \
  -DWITH_ASTYLE=OFF \
  -DWITH_DESKTOP=ON \
  -DWITH_BINDINGS=ON \
+ -DWITH_SERVER=ON \
  -DDISABLE_DEPRECATED=ON \
  -DCXX_EXTRA_FLAGS=${CLANG_WARNINGS} ..
 echo "travis_fold:end:cmake"