Don't explicitly specify streams to docker run.

Now that "docker run" always has an stdin, we don't need to explicitly
specify stdout and stderr.

plugins/00_dokku-standard/commands

@@ -51,7 +51,7 @@ case "$1" in
         exit 1
     fi
     shift 2
-    docker run -i -t -a stdout -a stderr $IMAGE /exec "$@"
+    docker run -i -t $IMAGE /exec "$@"
     ;;
 
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