chore: update readme and issue template

Author: woothu

ISSUE_TEMPLATE.md

@@ -1,7 +1,7 @@
 # Before opening an issue
 
 - [Search for duplicate or closed issues](https://github.com/coreui/coreui-vue/issues?q=is%3Aissue+is%3Aclosed)
-- Read the [contributing guidelines](https://github.com/coreui/coreui-vue/blob/v3-next/CONTRIBUTING.md)
+- Read the [contributing guidelines](https://github.com/coreui/coreui-vue/blob/master/CONTRIBUTING.md)
 
 When asking general "how to" questions:
 

README.md

@@ -3,7 +3,7 @@
 [![Tweet](https://img.shields.io/twitter/url/http/shields.io.svg?style=social)](https://twitter.com/intent/tweet?text=CoreUI%20-%20Free%20Vue%20Admin%20Template%20&url=http://coreui.io/vue/&hashtags=bootstrap,admin,template,dashboard,panel,free,angular,react,vue)
 [![NPM][npm-coreui-vue-badge-latest]][npm-coreui-vue]
 [![Downloads](https://img.shields.io/npm/dm/@coreui/vue.svg?style=flat-square)][coreui]
-[![Build](https://img.shields.io/github/workflow/status/coreui/coreui-vue/Node%20CI/v3-next?style=flat-square)][coreui]
+[![Build](https://img.shields.io/github/workflow/status/coreui/coreui-vue/Node%20CI/master?style=flat-square)][coreui]
 [![License](https://img.shields.io/npm/l/@coreui/vue?style=flat-square)][coreui]
 [![Coverage](https://img.shields.io/badge/test%20coverage%203.0.0%20version-100%25-yellowgreen)][coreui]
 
@@ -105,7 +105,7 @@ See the GitHub [release history](https://github.com/coreui/coreui-vue/releases).
 
 ### Contributing
 
-See [CONTRIBUTING.md](https://github.com/coreui/coreui-vue/blob/v3-next/CONTRIBUTING.md).
+See [CONTRIBUTING.md](https://github.com/coreui/coreui-vue/blob/master/CONTRIBUTING.md).
 
 ### Credits