Fixed reference error exception

- Since self.session.close() in __del__ is a weak reference, python 3 may issue an uncaught exception since it has already been cleared.  The try/except handles it.

Author: Chris Park

rosette/api.py

@@ -609,7 +609,10 @@ def __init__(
         }
 
     def __del__(self):
-        self.session.close()
+        try:
+            self.session.close()
+        except ReferenceError:
+            pass
 
     def _set_pool_size(self):
         adapter = requests.adapters.HTTPAdapter(