deps: update pytest from 4.3.0 to 4.3.1

Update pytest from 4.3.0 to 4.3.1 (#31)

requirements.txt

@@ -1,4 +1,4 @@
 mock==2.0.0
 pylint==1.9.3
-pytest==4.3.0
+pytest==4.3.1
 snapshottest==0.5.0