Update ICU verision in README to 66.1.

Bug: 149845726
Test: n/a
Change-Id: I657a1c0b5df62b88562b93ccb3011b64ef4fbfa2
diff --git a/README.version b/README.version
index 27e4b61..e62fad0 100644
--- a/README.version
+++ b/README.version
@@ -1,3 +1,3 @@
 URL: https://github.com/unicode-org/icu
-Version: 64.2
+Version: 66.1
 BugComponent: 23970