deps: update core dependencies (#198)

Author: renovate-bot

pom.xml

@@ -153,14 +153,14 @@
     <site.installationModule>google-cloud-core-parent</site.installationModule>
     <auto-value.version>1.7</auto-value.version>
     <auto-value-annotations.version>1.7</auto-value-annotations.version>
-    <gax.version>1.54.0</gax.version>
+    <gax.version>1.55.0</gax.version>
     <google.api-common.version>1.9.0</google.api-common.version>
     <google.common-protos.version>1.17.0</google.common-protos.version>
     <google.iam.version>0.13.0</google.iam.version>
     <google.auth.version>0.20.0</google.auth.version>
     <google.api.version>1.30.9</google.api.version>
     <google.http.version>1.34.2</google.http.version>
-    <grpc.version>1.27.2</grpc.version>
+    <grpc.version>1.28.1</grpc.version>
     <protobuf.version>3.11.4</protobuf.version>
     <opencensus.version>0.24.0</opencensus.version>
     <annotations-api.version>1.3.2</annotations-api.version>