add if for test case

Author: yongwww

tests/python/frontend/tensorflow/test_forward.py

@@ -1249,7 +1249,8 @@ def test_forward_rel_ops():
     test_forward_pad()
     test_forward_gather()
     # Gather was used in tf 1.6 and before
-    # test_forward_gather_v1()
+    if int(tf.__version__.split('.')[1]) <= 6:
+        test_forward_gather_v1()
     test_forward_stridedslice()
     test_forward_split()
     test_forward_unstack()