Update setup.py

Author: rllin

setup.py

@@ -16,7 +16,7 @@
     install_requires=[
         "backoff==1.10.0",
         "backports-datetime-fromisoformat==1.0.0",
-        "dataclasses==0.7",
+        "dataclasses==0.7; python_version < '3.7.0'",
         "ndjson==0.3.1",
         "requests>=2.22.0",
         "google-api-core>=1.22.1",