Add go release 1.11.3 to client_matrix.py
diff --git a/tools/interop_matrix/client_matrix.py b/tools/interop_matrix/client_matrix.py
index c45a627..7b4b234 100644
--- a/tools/interop_matrix/client_matrix.py
+++ b/tools/interop_matrix/client_matrix.py
@@ -120,7 +120,7 @@
             'v1.10.1': None
         },
         {
-            'v1.11.1': None
+            'v1.11.3': None
         },
     ],
     'java': [