Fix graph scrolling bug

app/assets/stylesheets/pages/pipelines.scss

@@ -232,20 +232,21 @@
 
 // Pipeline visualization
 
-.pipeline-visualization {
-  position: relative;
+.pipeline-graph {
   width: 100%;
   overflow: auto;
+  white-space: nowrap;
+}
+
+.pipeline-visualization {
+  position: relative;
+  min-width: 1220px;
 
   ul {
     padding: 0;
   }
 }
 
-.stage-column-list {
-  min-width: 1220px;
-}
-
 .stage-column {
   display: inline-block;
   vertical-align: top;

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

-.row-content-block.white
-
+.row-content-block.build-content.middle-block.pipeline-graph
   .pipeline-visualization
     %ul.stage-column-list
       - pipeline.statuses.stages.each do |stage|
@@ -19,7 +18,7 @@
                       = ci_icon_for_status(status)
                     = build.name
 
-.row-content-block.build-content.middle-block
+.row-content-block.build-content.middle-block.pipeline-graph
   .pull-right
     - if can?(current_user, :update_pipeline, pipeline.project)
       - if pipeline.builds.latest.failed.any?(&:retryable?)