deps: update dependency io.grpc:grpc-bom to v1.28.1 (#250)

pom.xml

@@ -103,7 +103,7 @@
       <dependency>
         <groupId>io.grpc</groupId>
         <artifactId>grpc-bom</artifactId>
-        <version>1.27.0</version>
+        <version>1.28.1</version>
         <type>pom</type>
         <scope>import</scope>
       </dependency>