Fix typo in client.py.j2 (#18)

Author: michaelbausor

packages/gapic-generator/gapic/templates/$namespace/$name_$version/$service/client.py.j2

@@ -67,7 +67,7 @@ class {{ service.name }}:
                 should be retried.
             timeout (float): The timeout for this request.
             metadata (Sequence[Tuple[str, str]]): Strings which should be
-                sent alont with the request as metadata.
+                sent along with the request as metadata.
 
         Returns:
             {{ method.output.sphinx_ident }}: