bump grpc version (#3447)

Author: yihanzhen

google-cloud-clients/pom.xml

@@ -158,12 +158,12 @@
     <api-client.version>1.23.0</api-client.version>
     <gax.version>1.29.0</gax.version>
     <google.auth.version>0.9.1</google.auth.version>
-    <grpc.version>1.12.0</grpc.version>
+    <grpc.version>1.13.1</grpc.version>
     <nettyssl.version>2.0.7.Final</nettyssl.version>
     <guava.version>20.0</guava.version>
     <http-client.version>1.23.0</http-client.version>
     <protobuf.version>3.5.1</protobuf.version>
-    <opencensus.version>0.11.1</opencensus.version>
+    <opencensus.version>0.12.3</opencensus.version>
     <!-- test dependency versions -->
     <easymock.version>3.4</easymock.version>
     <objenesis.version>2.6</objenesis.version>