gradle: update butterknife to 9.0.0rc2

Change-Id: I7289b9f9439ac6af2e00597d6b78ed54b3fe2340
diff --git a/ring-android/app/build.gradle b/ring-android/app/build.gradle
index fdc01f3..bbc5f0a 100644
--- a/ring-android/app/build.gradle
+++ b/ring-android/app/build.gradle
@@ -67,7 +67,7 @@
 dependencies {
     def android_support_version = '1.0.0'
     def material_version = '1.0.0'
-    def butterknife_version = "9.0.0-rc1"
+    def butterknife_version = "9.0.0-rc2"
     def dagger_version = "2.17"
 
     implementation fileTree(include: '*.jar', dir: 'libs')