deps: update pytest from 4.0.0 to 4.0.1

Update pytest from 4.0.0 to 4.0.1 (#18)

requirements.txt

@@ -1,4 +1,4 @@
 mock==2.0.0
 pylint==1.9.3
-pytest==4.0.0
+pytest==4.0.1
 snapshottest==0.5.0