move contributing guide to github meta directory

Author: kazupon

CONTRIBUTING.md renamed to .github/CONTRIBUTING.md

@@ -10,7 +10,7 @@
 
   - For simple beginner questions, you can get quick answers from [`#vue-i18n` channel of Discord](https://chat.vuejs.org/)
 
-- Try to search for your issue, it may have already been answered or even fixed in the development branch.
+- Try to search for your issue, it may have already been answered or even fixed in the master branch.
 
 - Check if the issue is reproducible with the latest stable version of vue-i18n-extensions. If you are using a pre-release, please indicate the specific version you are using.
 
@@ -24,7 +24,7 @@
 
 - The `master` branch is basically just a snapshot of the latest stable release. All development should be done in dedicated branches. **Do not submit PRs against the `master` branch.**
 
-- Checkout a topic branch from the relevant branch, e.g. `dev`, and merge back against that branch.
+- Checkout a topic branch from the relevant branch, e.g. `master`, and merge back against that branch.
 
 - Work in the `src` folder and **DO NOT** checkin `dist` in the commits.
 
@@ -42,11 +42,11 @@
 
 ### Work Step Example
 - Fork the repository from [kazupon/vue-i18n-extensions](https://github.com/kazupon/vue-i18n-extensions) !
-- Create your topic branch from `dev`: `git branch my-new-topic origin/dev`
+- Create your topic branch from `master`: `git branch my-new-topic origin/master`
 - Add codes and pass tests !
 - Commit your changes: `git commit -am 'Add some topic'`
 - Push to the branch: `git push origin my-new-topic`
-- Submit a pull request to `dev` branch of `kazupon/vue-i18n-extensions` repository !
+- Submit a pull request to `master` branch of `kazupon/vue-i18n-extensions` repository !
 
 ## Development Setup