modify shebang to bash after install if bash is installed.

dnsapi/dns_cf.sh

@@ -1,4 +1,4 @@
-#!/usr/bin/env bash
+#!/usr/bin/env sh
 
 
 #

dnsapi/dns_cx.sh

@@ -1,4 +1,4 @@
-#!/usr/bin/env bash
+#!/usr/bin/env sh
 
 # Cloudxns.com Domain api
 #

dnsapi/dns_dp.sh

@@ -1,4 +1,4 @@
-#!/usr/bin/env bash
+#!/usr/bin/env sh
 
 # Dnspod.cn Domain api
 #

dnsapi/dns_myapi.sh

@@ -1,4 +1,4 @@
-#!/usr/bin/env bash
+#!/usr/bin/env sh
 
 #Here is a sample custom api script.
 #This file name is "dns_myapi.sh"