Fix over-indentation in exceptions.py

Signed-off-by: Toby Harradine <tobyharradine@gmail.com>

Author: Tobotimus

aiohttp_json_rpc/exceptions.py

@@ -21,7 +21,7 @@ def __init__(self, *args, msg_id=None, data=None, error_code=None,
 
         if(error_code is not None and
            error_code not in self.lookup_table.keys()):
-                raise ValueError('error code out of range')
+            raise ValueError('error code out of range')
 
         self.data = data
         self.msg_id = msg_id