Update readme for release 8.13.6 (#2886)

diff --git a/README.md b/README.md
index 4ff8e09..8664581 100644
--- a/README.md
+++ b/README.md
@@ -55,7 +55,7 @@
 The [Java demo](https://libphonenumber.appspot.com/) is updated with a slight
 delay after the GitHub release.
 
-Last demo update: v8.13.5.
+Last demo update: v8.13.6.
 
 Note: Eventhough the library (main branch/[maven release](https://repo1.maven.org/maven2/com/googlecode/libphonenumber/libphonenumber/8.12.56/))
 is at v8.12.57, because of some deployment issues, we were unable to update the