Update to google-auth-library-java 0.13.0

0.13.0 is the latest version.

This honestly doesn't do much since any user of our auth API will be
depending on the library themselves (we only depend on the interface; no
implementation). But getting past 0.9.1 may encourage our users to use a
newer version with better JWT handling and 0.9.1 was released 10 months
ago, so we're overdue for an update.

Fixes grpc#4700

build.gradle

@@ -108,7 +108,7 @@ subprojects {
         javaPluginPath = "$rootDir/compiler/build/exe/java_plugin/$protocPluginBaseName$exeSuffix"
 
         nettyVersion = '4.1.32.Final'
-        googleauthVersion = '0.9.0'
+        googleauthVersion = '0.13.0'
         guavaVersion = '26.0-android'
         protobufVersion = '3.6.1'
         protocVersion = protobufVersion