Fixed links in CONTRIBUTING.md

.github/CONTRIBUTING.md

@@ -1,7 +1,7 @@
 Contributing to Yii2
 ====================
 
-- [Report an issue](docs/internals/report-an-issue.md)
-- [Translate documentation or messages](docs/internals/translation-workflow.md)
+- [Report an issue](https://github.com/yiisoft/yii2/blob/master/docs/internals/report-an-issue.md)
+- [Translate documentation or messages](https://github.com/yiisoft/yii2/blob/master/docs/internals/translation-workflow.md)
 - [Give us feedback or start a design discussion](http://www.yiiframework.com/forum/index.php/forum/42-general-discussions-for-yii-20/)
-- [Contribute to the core code or fix bugs](docs/internals/git-workflow.md)
+- [Contribute to the core code or fix bugs](https://github.com/yiisoft/yii2/blob/master/docs/internals/git-workflow.md)