[ci skip] Fix UX Guide link on Contributing.md

CONTRIBUTING.md

@@ -9,8 +9,6 @@
     - [Helping others](#helping-others)
     - [I want to contribute!](#i-want-to-contribute)
     - [Implement design & UI elements](#implement-design-ui-elements)
-        - [Design reference](#design-reference)
-        - [UI development kit](#ui-development-kit)
     - [Issue tracker](#issue-tracker)
         - [Feature proposals](#feature-proposals)
         - [Issue tracker guidelines](#issue-tracker-guidelines)
@@ -90,7 +88,7 @@ This was inspired by [an article by Kent C. Dodds][medium-up-for-grabs].
 
 ## Implement design & UI elements
 
-Please see the [UI Guide for building GitLab].
+Please see the [UX Guide for GitLab].
 
 ## Issue tracker
 
@@ -469,5 +467,5 @@ available at [http://contributor-covenant.org/version/1/1/0/](http://contributor
 [doc-styleguide]: doc/development/doc_styleguide.md "Documentation styleguide"
 [scss-styleguide]: doc/development/scss_styleguide.md "SCSS styleguide"
 [newlines-styleguide]: doc/development/newlines_styleguide.md "Newlines styleguide"
-[UI Guide for building GitLab]: https://gitlab.com/gitlab-org/gitlab-ce/blob/master/doc/development/ui_guide.md
+[UX Guide for GitLab]: http://docs.gitlab.com/ce/development/ux_guide/
 [license-finder-doc]: doc/development/licensing.md