Update README.version to have correct version.

Test: None
diff --git a/README.version b/README.version
index 9028caa..eb0b315 100644
--- a/README.version
+++ b/README.version
@@ -1,4 +1,4 @@
 URL: https://github.com/checkstyle/checkstyle
-Version: 7.4-SNAPSHOT
+Version: 8.1
 BugComponent: 156049
 Owners: aurimas