build: Upgrade gradle to 6.4.1 and dependencies to latest versions

Change-Id: I949dce4b11cb28b7230085de7124d489f93c94f6
diff --git a/build.gradle b/build.gradle
index b61a985..f782363 100644
--- a/build.gradle
+++ b/build.gradle
@@ -12,7 +12,7 @@
         }
     }
     dependencies {
-        classpath 'com.android.tools.build:gradle:3.4.0'
+        classpath 'com.android.tools.build:gradle:4.0.0'
         // classpath 'net.named-data.playground:play-publisher:1.2.0-2-SNAPSHOT'
         classpath 'com.github.triplet.gradle:play-publisher:2.2.1'