Fix build --prod depreciated warning

Dockerfile

@@ -4,7 +4,7 @@ COPY . /src
 
 WORKDIR /src/src-ui
 RUN npm install
-RUN ./node_modules/.bin/ng build --prod
+RUN ./node_modules/.bin/ng build --configuration production
 
 
 FROM ubuntu:20.04 AS jbig2enc

docs/extending.rst

@@ -65,7 +65,7 @@ To do the setup you need to perform the steps from the following chapters in a c
     .. code:: shell-session
 
         npm install .
-        ./node_modules/.bin/ng build --prod
+        ./node_modules/.bin/ng build --configuration production
 
 8.  Apply migrations and create a superuser for your dev instance: