Fix typo in currentMembershipsExist check

Author: lodewiges

app/templates/users/user/groups.hbs

@@ -10,7 +10,7 @@
           <a
             class='nav-link
               {{if this.currentMembershipsSelected "active"}}
-              {{if (not this.currentmembershipsExist) "disabled"}}'
+              {{if (not this.currentMembershipsExist) "disabled"}}'
             {{on 'click' selectCurrentMemberships}}
           >
             Huidige groepen
@@ -85,4 +85,4 @@
       </div>
     {{/each}}
   </div>
-</TabbedView>
+</TabbedView>