Fix requirements. (#615)

Author: gtopper

clients/py/requirements.txt

@@ -1,6 +1,6 @@
 googleapis-common-protos>=1.5.3
 # Can be loosened, but grpcio 1.34.0 must not be used as it segfaults (1.34.1 ok).
-grpcio-tools>=1.30<1.33
-grpcio>=1.30<1.33
+grpcio-tools>=1.30,<1.33
+grpcio>=1.30,<1.33
 pandas>=0.23.4
 requests>=2.19.1