Updated changelog and requirements regarding ckan 2.10 upgrade

CHANGELOG.md

@@ -16,6 +16,10 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 - Removed language field from dataset form.
 
+### Changed
+
+- Minimum ckan version changed from `2.9` to `2.10` (requires `ckan db upgrade`)
+
 ## [2.1.0]
 
 ### Added

requirements.txt

-ckan
+ckan~=2.10.0
 ckanext-harvest
 ckanext-spatial
 lxml