update docker string

Makefile

@@ -30,7 +30,7 @@ subnotebooks: $(SUBNOTEBOOKS)
 
 %.pdf: %.html $(DEP_PRESENTATION)
 	# This needs to have artificially large paper size in order to fix bug https://github.com/astefanutti/decktape/issues/151#issuecomment-456166075
-	docker run --rm -t -v $(PWD):/slides astefanutti/decktape --size "2560x1440" reveal $< $@
+	docker run --rm -t --user $(id -u $USER):$(id -g $USER) -v $(PWD):/slides astefanutti/decktape --size "2560x1440" reveal $< $@
 
 Introduction-to-Pandas--slides.ipynb: $(MASTER_NOTEBOOK)
 	notebook-splitter --keep task --keep solution --keep onlypresentation --remove onlytask --remove onlysolution --remove nopresentation -o $@ $<