deps: update dependency io.grpc:grpc-bom to v1.28.1 (#132)

Author: renovate-bot

pom.xml

@@ -70,7 +70,7 @@
     <gax.version>1.55.0</gax.version>
     <auto-value-annotations.version>1.7</auto-value-annotations.version>
     <jackson-core.version>2.10.3</jackson-core.version>
-    <grpc.version>1.28.0</grpc.version>
+    <grpc.version>1.28.1</grpc.version>
     <protobuf.version>3.11.4</protobuf.version>
     <junit.version>4.13</junit.version>
     <guava.version>28.2-android</guava.version>