docs: README build status badge (#23933)

* fixed build status badge

* changed build branch from `master` to `develop`

* updated build status badge url

* Update README.md
diff --git a/README.md b/README.md
index 0f6a521..15782a2 100644
--- a/README.md
+++ b/README.md
@@ -5,7 +5,7 @@
         <p>ERP made simple</p>
     </p>
 
-[![Build Status](https://travis-ci.com/frappe/erpnext.svg)](https://travis-ci.com/frappe/erpnext)
+[![Build Status](https://api.travis-ci.com/frappe/erpnext.svg?branch=develop)](https://travis-ci.com/frappe/erpnext)
 [![Open Source Helpers](https://www.codetriage.com/frappe/erpnext/badges/users.svg)](https://www.codetriage.com/frappe/erpnext)
 [![Coverage Status](https://coveralls.io/repos/github/frappe/erpnext/badge.svg?branch=develop)](https://coveralls.io/github/frappe/erpnext?branch=develop)