Fix issue where build fails with no dist folder

Change-Id: I38e64f5aeb0a67986f419434fcff9bea2bf420c9
diff --git a/Makefile b/Makefile
index 4d774f1..da864d1 100644
--- a/Makefile
+++ b/Makefile
@@ -34,7 +34,7 @@
 
 dist:
 	@ echo "Creating python source distribution"
-	rm -r dist/
+	rm -rf dist/
 	python setup.py sdist
 
 upload: dist