Update syntax

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

-- show_whitespace_toggle = local_assigns.fetch :show_whitespace_toggle, true
+- show_whitespace_toggle = local_assigns.fetch(:show_whitespace_toggle, true)
 - if diff_view == 'parallel'
   - fluid_layout true
 
@@ -9,7 +9,7 @@
     - if show_whitespace_toggle
       - if current_controller?(:commit)
         = commit_diff_whitespace_link(@project, @commit)
-      - if current_controller?(:merge_requests)
+      - elsif current_controller?(:merge_requests)
         = diff_merge_request_whitespace_link(@project, @merge_request)
     .btn-group
       = inline_diff_btn