Shorten merge request WIP text.

CHANGELOG

 Please view this file on the master branch, on stable branches it's out of date.
 v 7.12.0 (unreleased)
+  - Shorten merge request WIP text.
   - Refactor permission checks with issues and merge requests project settings (Stan Hu)
   - Fix Markdown preview not working in Edit Milestone page (Stan Hu)
   - Fix Zen Mode not closing with ESC key (Stan Hu)

app/views/projects/_issuable_form.html.haml

@@ -15,11 +15,11 @@
     - if issuable.is_a?(MergeRequest)
       %p.help-block
         - if issuable.work_in_progress?
-          This merge request is marked a <strong>Work In Progress</strong>.
-          When it's ready, remove the <code>WIP</code> prefix from the title to allow it to be accepted.
+          Remove the <code>WIP</code> prefix from the title to allow this 
+          <strong>Work In Progress</strong> merge request to be accepted when it's ready.
         - else
-          To prevent this merge request from being accepted before it's ready,
-          mark it a <strong>Work In Progress</strong> by starting the title with <code>[WIP]</code> or <code>WIP:</code>.
+          Start the title with <code>[WIP]</code> or <code>WIP:</code> to prevent a 
+          <strong>Work In Progress</strong> merge request from being accepted before it's ready.
 .form-group.issuable-description
   = f.label :description, 'Description', class: 'control-label'
   .col-sm-10