Add changelog entry

Author: jamesls

.changes/next-release/enhancement-EnvironmentVariables-90061.json

@@ -0,0 +1,5 @@
+{
+  "category": "Environment Variables", 
+  "type": "enhancement", 
+  "description": "Ignore env var credentials is values are empty (`#1680 <https://github.com/boto/botocore/issues/1680>`__)"
+}