Dockerfile: have UTF8 defined

git-svn-id: https://svn.osgeo.org/grass/grass/trunk@73400 15284696-431f-4ddb-bdfa-cd5b030d7da7

Dockerfile

@@ -65,6 +65,8 @@ RUN apt-get update \
     mkdir -p $DATA_DIR
 
 RUN echo LANG="en_US.UTF-8" > /etc/default/locale
+ENV LANG C.UTF-8
+ENV LC_ALL C.UTF-8
 
 RUN mkdir /code
 RUN mkdir /code/grass