Update pip from 8.1.2 to 9.0.1

pyup-bot · pyup-bot · commit 00464a8a1cc4 · 2017-05-24T12:20:48.000+02:00
diff --git a/requirements_dev.txt b/requirements_dev.txt
@@ -1,4 +1,4 @@
-pip==8.1.2
+pip==9.0.1
 bumpversion==0.5.3
 wheel==0.29.0
 watchdog==0.8.3
