Fix regexp in test_request_headers test

It didn't account that ably-python versions can have multiple digits for major/minor/patch parts

Author: VeskeR

test/ably/rest/resthttp_test.py

@@ -192,7 +192,7 @@ async def test_request_headers(self):
 
         # Agent
         assert 'Ably-Agent' in r.request.headers
-        expr = r"^ably-python\/\d.\d.\d(-beta\.\d)? python\/\d.\d+.\d+$"
+        expr = r"^ably-python\/\d+.\d+.\d+(-beta\.\d+)? python\/\d.\d+.\d+$"
         assert re.search(expr, r.request.headers['Ably-Agent'])
         await ably.close()