Bump docker from 3.5.1 to 4.0.2 (#594)

dependabot-preview[bot] · web-flow · commit 86624f823090 · 2019-09-20T18:04:19.000Z
diff --git a/requirements.txt b/requirements.txt
@@ -1,5 +1,5 @@
 coverage==4.5.1
-docker==3.5.1
+docker==4.0.2
 flake8==3.5.0
 -e .[sa]
 sphinx==2.2.0
