Bump default resolver to 9.12

Porges · Porges · commit 399c63542d70 · 2017-11-06T21:09:16.000+11:00
diff --git a/stack.yaml b/stack.yaml
@@ -3,4 +3,4 @@ extra-package-dbs: []
 packages:
 - '.'
 extra-deps: []
-resolver: lts-9.0
+resolver: lts-9.12
