Bump deps versions for AGP, truth, errorprone, findbugs, etc.
diff --git a/gradle.properties b/gradle.properties
index f2598ed..f6d41e1 100644
--- a/gradle.properties
+++ b/gradle.properties
@@ -1,3 +1,6 @@
 thisVersion=4.0-beta-2-SNAPSHOT
 
 apiCompatVersion=3.8
+
+errorproneVersion=2.3.1
+errorproneJavacVersion=9+181-r4173-1