Explicitly set MODE

Co-author: @MikiDi

Author: madnificent

Dockerfile

@@ -18,6 +18,7 @@ ENV LOG_SPARQL_ALL True
 ENV MU_SPARQL_ENDPOINT 'http://database:8890/sparql'
 ENV MU_SPARQL_UPDATEPOINT 'http://database:8890/sparql'
 ENV MU_APPLICATION_GRAPH 'http://mu.semte.ch/application'
+ENV MODE 'production'
 
 RUN mkdir -p /usr/src/app
 WORKDIR /usr/src/app