deps: update core dependencies (#215)

Author: renovate-bot

google-cloud-bigtable-deps-bom/pom.xml

@@ -76,11 +76,11 @@
  <gax.version>1.54.0</gax.version>
  <google.api-common.version>1.8.1</google.api-common.version>
  <google.common-protos.version>1.17.0</google.common-protos.version>
- <google.core.version>1.93.1</google.core.version>
+ <google.core.version>1.93.2</google.core.version>
  <google.auth.version>0.20.0</google.auth.version>
  <google-http-client.version>1.34.2</google-http-client.version>
  <!-- make sure to update the grpc version in README -->
- <grpc.version>1.27.2</grpc.version>
+ <grpc.version>1.28.0</grpc.version>
  <guava.version>28.2-android</guava.version>
  <opencensus.version>0.25.0</opencensus.version>
  <protobuf.version>3.11.4</protobuf.version>