Don't show `Responsibilities` header, if there aren't any (#540)

layouts/partials/sections/experiences/single-position.html

@@ -12,10 +12,12 @@
     <!-- Add company overview -->
     <p>{{ .company.overview | markdownify }}</p>
     <!-- Add the responsibilities handled at this position -->
+    {{ if $position.responsibilities }}
     <h6 class="text-muted">{{ i18n "responsibilities" }}</h6>
     <ul class="justify-content-around">
     {{ range $position.responsibilities }}
         <li>{{ . | markdownify }}</li>
     {{ end }}
     </ul>
+    {{ end }}
 </div>