feat: prefix error message with ERROR

CHANGELOG.md

@@ -13,6 +13,10 @@ Which is based on [Keep A Changelog](http://keepachangelog.com/)
 - Generate random password
 - Print the expiration time of TOTP code
 
+## Changed
+
+- Prefix error message with ERROR 
+
 ## v1.0.0 - 2019-07-12
 
 ### Added

gpm/cli.go

@@ -90,7 +90,7 @@ func (c *Cli) generatePassword(length int, letter bool, digit bool, special bool
 
 // error print a message and exit)
 func (c *Cli) error(msg string) {
-  fmt.Println(msg)
+  fmt.Printf("ERROR: %s\n", msg)
   os.Exit(2)
 }