python 3.7 compatibility

https://docs.python.org/3/reference/datamodel.html#async-iterators

Author: dariko

etcd3/aio_client.py

@@ -74,7 +74,7 @@ async def __aenter__(self):
     async def __aexit__(self, exc_type, exc_val, exc_tb):
         self.close()
 
-    async def __aiter__(self):
+    def __aiter__(self):
         return self
 
     async def __anext__(self):
@@ -112,7 +112,7 @@ def __init__(self, resp):
         self.left_chunk = b''
         self.i = 0
 
-    async def __aiter__(self):
+    def __aiter__(self):
         return self
 
     async def next(self):