Updated changelog

Author: tleguijt

CHANGES

@@ -3,6 +3,8 @@ x.x.x (unreleased)
 - Re-generated schemas and types
 - Removed Optional type from get_by_id calls
 - Correctly use Optional typing according to RAML source file
+- Improved error information in CommercetoolsError object
+- Testing: Add setAttribute and addVariant actions to product testing backend
 - Testing: Add addAttributeDefinition action to testing backend
 - Testing: Check for unique values in testing backend
 - Testing: Fixed Attribute return object in ProductTypes testing backend