deps: update dependency com.google.guava:guava-bom to v28.2-android (#113)

Author: renovate-bot

pom.xml

@@ -163,7 +163,7 @@
     <protobuf.version>3.11.1</protobuf.version>
     <opencensus.version>0.24.0</opencensus.version>
     <annotations-api.version>1.3.2</annotations-api.version>
-    <guava.version>28.1-android</guava.version><!-- We are currently using the *-android version to support JDK7. -->
+    <guava.version>28.2-android</guava.version><!-- We are currently using the *-android version to support JDK7. -->
     <junit.version>4.12</junit.version>
     <truth.version>1.0</truth.version>
     <easymock.version>3.6</easymock.version>