Bump `cmk` version to v6.4.0

Signed-off-by: Rohit Yadav <rohit.yadav@shapeblue.com>
diff --git a/CHANGES.md b/CHANGES.md
index 070febd..9dadbf6 100644
--- a/CHANGES.md
+++ b/CHANGES.md
@@ -1,6 +1,18 @@
 Apache CloudStack CloudMonkey Changelog
 ---------------------------------------
 
+Version 6.4.0
+=============
+This release includes:
+- Improve CLI mode usage and output handling
+- Add support for http POST handling for password and user-data
+- Optimise async API jobs polling
+- Better interrupt handling of Ctrl+C to cancel on-going API request but not
+  crash `cmk`
+- Remove unnecessary call to listApis (sync) when using CLI mode with url,
+  api key, secret key
+- Updates inbuilt API precache to ACS v4.19
+
 Version 6.3.0
 =============
 This release includes:
diff --git a/config/about.go b/config/about.go
index a167601..153bbef 100644
--- a/config/about.go
+++ b/config/about.go
@@ -26,7 +26,7 @@
 
 // Version CLI
 func (c *Config) Version() string {
-	return "6.4.0-rc"
+	return "6.4.0"
 }
 
 // PrintHeader prints startup message in CLI mode