Add transition CSS to job hovers

In the new pipeline graph layout with dependencies, if
the user hover between jobs, it used to flicker because
there was no transition. This commit adds transition on
job components.

app/assets/javascripts/pipelines/components/graph/stage_column_component.vue

@@ -160,7 +160,10 @@ export default {
           :pipeline-id="pipelineId"
           :stage-name="showStageName ? group.stageName : ''"
           css-class-job-name="gl-build-content"
-          :class="{ 'gl-opacity-3': isFadedOut(group.name) }"
+          :class="[
+            { 'gl-opacity-3': isFadedOut(group.name) },
+            'gl-transition-duration-slow gl-transition-timing-function-ease',
+          ]"
           @pipelineActionRequestComplete="$emit('refreshPipelineGraph')"
         />
         <div v-else-if="isParallel(group)" :class="{ 'gl-opacity-3': isFadedOut(group.name) }">