Fix broken link

[ynden]

Description

In vuepress config, the docBranch property is set to master.
I changed it to use the current default branch (i.e: dev).

Fixes: #1527

Purpose

This pull request is a:

• Bugfix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)

Checklist

• I have added tests that prove my fix is effective or that my feature works
• I have added necessary documentation (if appropriate)

[alexeyzimarev]

Thanks!