fix: typo in success message (#340)

Reflects changes made by [drone-ssh#283](appleboy/drone-ssh#283)

Author: 1ukastesar

README.md

@@ -82,9 +82,9 @@ output:
 whoami
 ======END======
 out: ***
-==============================================
-✅ Successfully executed commands to all host.
-==============================================
+===============================================
+✅ Successfully executed commands to all hosts.
+===============================================
 ```
 
 ### Setting up a SSH Key

README.zh-cn.md

@@ -74,9 +74,9 @@ jobs:
 whoami
 ======END======
 out: ***
-==============================================
-✅ Successfully executed commands to all host.
-==============================================
+===============================================
+✅ Successfully executed commands to all hosts.
+===============================================
 ```
 
 ### 设置 SSH 密钥

README.zh-tw.md

@@ -74,9 +74,9 @@ jobs:
 whoami
 ======END======
 out: ***
-==============================================
-✅ Successfully executed commands to all host.
-==============================================
+===============================================
+✅ Successfully executed commands to all hosts.
+===============================================
 ```
 
 ### 設置 SSH 金鑰