SW-860: build faster with 6 parallel jobs

.gitlab-ci.yml

@@ -27,7 +27,7 @@ build_RAServices:
     - mkdir -p build/gnucxx11_opt
     - cd build/gnucxx11_opt
     - cmake -DBUILD_PACKAGES=$PACKAGE -DCASACORE_ROOT_DIR=/opt/casacore/ -DCASAREST_ROOT_DIR=/opt/casarest/ -DCMAKE_INSTALL_PREFIX=/opt/lofar -DUSE_LOG4CPLUS=false ../..
-    - make
+    - make -j 6
     - make DESTDIR=../../install install
     - cd ../../install/opt/lofar
     - tar --ignore-failed-read --exclude=include -czf ../../RAServices_$CI_COMMIT_SHORT_SHA.ztar *