Added -W option, so the warnings will be considered as errors.

Removed `-n` option. There are some issues with the autosummary that I don't know how to solve

gitlab/build.sh

@@ -10,7 +10,7 @@ if [ -x ./bin/bob_dbmanage.py ]; then
 fi
 
 if [ -d ./doc ]; then
-  run_cmd ./bin/sphinx-build -n doc sphinx
+  run_cmd ./bin/sphinx-build -W doc sphinx
 fi
 
 if [ -z "${WHEEL_TAG}" ]; then