deps: update dependency com.google.guava:guava-bom to v28.2-android (#20)

Author: renovate-bot

pom.xml

@@ -70,7 +70,7 @@
     <grpc.version>1.27.0</grpc.version>
     <protobuf.version>3.11.1</protobuf.version>
     <junit.version>4.13</junit.version>
-    <guava.version>28.1-android</guava.version>
+    <guava.version>28.2-android</guava.version>
     <threeten.version>1.4.1</threeten.version>
     <javax.annotations.version>1.3.2</javax.annotations.version>
     <animal-sniffer.version>1.18</animal-sniffer.version>