Check imports with isort on drone

.drone.yml

@@ -6,6 +6,12 @@ build:
     commands:
       - XDG_CACHE_HOME=/drone/pip-cache pip install flake8
       - flake8 wagtail
+  isort:
+    image: python:3.5
+    commands:
+      - XDG_CACHE_HOME=/drone/pip-cache pip install wheel
+      - XDG_CACHE_HOME=/drone/pip-cache pip install isort -e .[testing,docs]
+      - isort --check-only --diff --recursive wagtail
   js:
     image: node:4.2.4
     commands:

setup.cfg

@@ -1,2 +1,6 @@
 [bdist_wheel]
 universal = 1
+
+[isort]
+line_length=100
+multi_line_output=4