about: bump version to next v6.4.0-(rc)

Signed-off-by: Rohit Yadav <rohit.yadav@shapeblue.com>
diff --git a/config/about.go b/config/about.go
index a8fd91c..a167601 100644
--- a/config/about.go
+++ b/config/about.go
@@ -26,7 +26,7 @@
 
 // Version CLI
 func (c *Config) Version() string {
-	return "6.3.0"
+	return "6.4.0-rc"
 }
 
 // PrintHeader prints startup message in CLI mode