deps: update dependency com.google.errorprone:error_prone_annotations to v2.6.0 (#412)

Author: renovate-bot

pom.xml

@@ -169,7 +169,7 @@
     <findbugs.version>3.0.2</findbugs.version>
     <threetenbp.version>1.5.0</threetenbp.version>
     <objenesis.version>2.6</objenesis.version>
-    <errorprone.version>2.5.1</errorprone.version>
+    <errorprone.version>2.6.0</errorprone.version>
     <gson.version>2.8.6</gson.version>
   </properties>