Show dashes when date is empty

app/assets/javascripts/cycle_analytics/components/total_time_component.js.es6

@@ -10,10 +10,15 @@
     },
     template: `
       <span class="total-time">
+        <template v-if="Object.keys(time).length">
           <template v-if="time.days">{{ time.days }} <span>{{ time.days === 1 ? 'day' : 'days' }}</span></template>
           <template v-if="time.hours">{{ time.hours }} <span>hr</span></template>
           <template v-if="time.mins && !time.days">{{ time.mins }} <span>mins</span></template>
           <template v-if="time.seconds && Object.keys(time).length === 1 || time.seconds === 0">{{ time.seconds }} <span>s</span></template>
+        </template>
+        <template v-else>
+          --
+        </template>
       </span>
     `,
   });