Work around react-pdf bug

Until diegomura/react-pdf#2400 is merged,
react-pdf can sometimes fall into an infinite loop during layouting,
when a min-presence-ahead element has a following sibling with vertical
margins. This caused our Star Wars example camp to be unprintable.
The bug does not happen with vertical padding, so this workaround will
fix the problem for now.

pdf/src/campPrint/scheduleEntry/ScheduleEntry.vue

@@ -37,7 +37,7 @@
       </View>
     </View>
   </View>
-  <View style="margin-bottom: 20pt; font-size: 10pt">
+  <View style="padding-bottom: 20pt; font-size: 10pt">
     <ContentNode :content-node="activity.rootContentNode()" />
   </View>
 </template>