Update version to v4.2.0

sugyan · sugyan · commit a74f3628ff8e · 2018-11-30T16:20:07.000+09:00
diff --git a/linebot/version.go b/linebot/version.go
@@ -16,4 +16,4 @@
 
 package linebot
 
-const version = "4.1.0"
+const version = "4.2.0"
