www: docker: Allow running composer as superuser

Change-Id: I58276259083677209efc99b52fb102bbc3fbe5c5
diff --git a/Dockerfile b/Dockerfile
index 8672c6f..0fd42f4 100644
--- a/Dockerfile
+++ b/Dockerfile
@@ -2,6 +2,7 @@
 
 ARG baseurl
 ENV full_baseurl=/$baseurl
+ENV COMPOSER_ALLOW_SUPERUSER=1
 
 WORKDIR /src
 ADD . /src