Typo in http.py exception message. (#602)

diff --git a/googleapiclient/http.py b/googleapiclient/http.py
index d62a5c1..4949d0c 100644
--- a/googleapiclient/http.py
+++ b/googleapiclient/http.py
@@ -1326,7 +1326,7 @@
     """
 
     if len(self._order) >= MAX_BATCH_LIMIT:
-      raise BatchError("Exceeded the maximum calls(%d) in a single bactch request."
+      raise BatchError("Exceeded the maximum calls(%d) in a single batch request."
                        % MAX_BATCH_LIMIT)
     if request_id is None:
       request_id = self._new_id()