Fix bug #111 Create Session kw prints Arg type

Convert the max_retries argument to integer using native python method int(), instead of the Robot convert_to_integer keyword. This avoid that garbage message is printed to Robot logs as: Argument types are: <type 'unicode'>

src/RequestsLibrary/RequestsKeywords.py

@@ -80,7 +80,7 @@ def _create_session(
         s.auth = auth if auth else s.auth
         s.proxies = proxies if proxies else s.proxies
 
-        max_retries = self.builtin.convert_to_integer(max_retries)        
+        max_retries = int(max_retries)        
 
         if max_retries > 0:
             http = requests.adapters.HTTPAdapter(max_retries=Retry(total=max_retries, backoff_factor=backoff_factor))