Update engine (#3214)

Also, update hello_android to use the new Java class names.
diff --git a/AUTHORS b/AUTHORS
index 35a5417..223d9a9 100644
--- a/AUTHORS
+++ b/AUTHORS
@@ -1,5 +1,5 @@
 # Below is a list of people and organizations that have contributed
-# to the Sky project. Names should be added to the list like so:
+# to the Flutter project. Names should be added to the list like so:
 #
 #   Name/Organization <email address>