Update version to v6.4.0

nasa9084 · nasa9084 · commit eee532af771c · 2019-10-29T12:47:53.000+09:00
diff --git a/linebot/version.go b/linebot/version.go
@@ -16,4 +16,4 @@
 
 package linebot
 
-const version = "6.3.0"
+const version = "6.4.0"
