more backtick strings

ui/src/components/DoorMapEditor.vue

@@ -6,7 +6,7 @@
       <ul>
         <li
           v-for="(step, index) in steps"
-          :key="'step-' + index"
+          :key="`step-${index}`"
           :class="current_step === index ? 'is-active' : ''"
           @click="change_step(index)"
         >

ui/src/components/door_map/DoorChooser.vue

@@ -10,13 +10,13 @@
       <ThouCanvas>
         <Rect
           v-for="(rect, index) in rectangles"
-          :key="'rect' + index"
+          :key="`rect-${index}`"
           :rectangle="rect"
           @click.left="choose_rect(index)"
         />
         <template
           v-for="(rect, index) in rectangles_chosen"
-          :key="'rect_chosen' + index"
+          :key="`rect_chosen-${index}`"
         >
           <Rect :rectangle="rect" :focused="true" />
           <RectText :rectangle="rect" :text="String(index)" />

ui/src/components/rects/RectPad.vue

@@ -10,7 +10,7 @@
   >
     <Rect
       v-for="(rect, index) in rectangles"
-      :key="'rect' + index"
+      :key="`rect-${index}`"
       :rectangle="rect"
     />
     <Rect