Fix email line-height in Outlook

Outlook seems to handle `white-space: pre` weirdly, so just use `pre`
elements (but only for emails!).

CHANGELOG

@@ -48,6 +48,7 @@ v 8.11.0 (unreleased)
   - Fix issue on empty project to allow developers to only push to protected branches if given permission
   - Add green outline to New Branch button. !5447 (winniehell)
   - Optimize generating of cache keys for issues and notes
+  - Fix repository push email formatting in Outlook
   - Improve performance of syntax highlighting Markdown code blocks
   - Update to gitlab_git 10.4.1 and take advantage of preserved Ref objects
   - Remove delay when hitting "Reply..." button on page with a lot of discussions

app/assets/stylesheets/mailers/repository_push_email.scss

@@ -45,7 +45,6 @@
 .line_content {
   padding-left: 0.5em;
   padding-right: 0.5em;
-  white-space: pre;
   &.old {
     background-color: $line-removed;
@@ -71,6 +70,10 @@
   }
 }
+pre {
+  margin: 0;
+}
+
 span.highlight_word {
   background-color: #fafe3d !important;
 }

app/views/notify/repository_push_email.html.haml

@@ -76,7 +76,7 @@
             - if blob && blob.respond_to?(:text?) && blob_text_viewable?(blob)
               %table.code.white
                 - diff_file.highlighted_diff_lines.each do |line|
-                  = render "projects/diffs/line", line: line, diff_file: diff_file, plain: true
+                  = render "projects/diffs/line", line: line, diff_file: diff_file, plain: true, email: true
             - else
               No preview for this file type
           %br

app/views/projects/diffs/_line.html.haml

+- email = local_assigns.fetch(:email, false)
 - plain = local_assigns.fetch(:plain, false)
 - type = line.type
 - line_code = diff_file.line_code(line) unless plain
@@ -22,4 +23,8 @@
         = link_text
       - else
         %a{href: "##{line_code}", data: { linenumber: link_text }}
-    %td.line_content.noteable_line{ class: type, data: (diff_view_line_data(line_code, diff_file.position(line), type) unless plain) }= diff_line_content(line.text, type)
+    %td.line_content.noteable_line{ class: type, data: (diff_view_line_data(line_code, diff_file.position(line), type) unless plain) }<
+      - if email
+        %pre= diff_line_content(line.text, type)
+      - else
+        = diff_line_content(line.text, type)