Update layer1.py

Author: Clement Demonchy

boto/beanstalk/layer1.py

@@ -773,7 +773,7 @@ def rebuild_environment(self, environment_id=None, environment_name=None):
             both.  If you do not specify either, AWS Elastic Beanstalk returns
             MissingRequiredParameter error.
 
-        :raises InvalidParameterValue: If the environment hadn't be created or is terminated
+        :raises InvalidParameterValue: If environment_name doesn't refer to a currently active environment
         :raises: InsufficientPrivilegesException
         """
         params = {}