Improve commit page style

Signed-off-by: Dmitriy Zaporozhets <dmitriy.zaporozhets@gmail.com>

app/assets/stylesheets/pages/commit.scss

@@ -47,11 +47,6 @@
 }
 
 .commit-box {
-  margin: 10px 0;
-  border-top: 1px solid #ddd;
-  border-bottom: 1px solid #ddd;
-  padding: 20px 0;
-
   .commit-title {
     margin: 0;
   }

app/views/projects/commit/_commit_box.html.haml

@@ -41,7 +41,7 @@
 .commit-info-row.branches
   %i.fa.fa-spinner.fa-spin
 
-.commit-box
+.commit-box.gray-content-block.middle-block
   %h3.commit-title
     = gfm escape_once(@commit.title)
   - if @commit.description.present?