Bug 1169939 - Switch .landscape.yaml to 2-space indent

.landscape.yaml

@@ -6,12 +6,11 @@ test-warnings: true
 strictness: medium
 max-line-length: 140
 uses:
-    - django
-    - celery
+  - django
+  - celery
 requirements:
-    - requirements/common.txt
-    - requirements/dev.txt
-
+  - requirements/common.txt
+  - requirements/dev.txt
 # We run flake8 (pep8 + pyflakes) as part of the Travis run,
 # so it's unnecessary to run them again here.
 pep8: