Support pickle for TomlTz. Fix #407 (#410)

toml/tz.py

diff --git a/toml/tz.py b/toml/tz.py
index bf20593..57b26a1 100644
--- a/toml/tz.py
+++ b/toml/tz.py
@@ -11,6 +11,9 @@
         self._hours = int(self._raw_offset[1:3])
         self._minutes = int(self._raw_offset[4:6])
 
+    def __getinitargs__(self):
+        return (self._raw_offset,)
+
     def __deepcopy__(self, memo):
         return self.__class__(self._raw_offset)