Add support for Date's

Fixes #47

lib/types/json-date.vue

@@ -0,0 +1,25 @@
+<script>
+export default {
+  name: 'JsonDate',
+  functional: true,
+  props: {
+    jsonValue: {
+      type: Date,
+      required: true
+    }
+  },
+  render (h, { props }) {
+    const value = props.jsonValue;
+
+    return h('span', {
+      class: {
+        'jv-item': true,
+        'jv-string': true,
+      },
+      domProps: {
+        innerText: `"${value.toLocaleString()}"`
+      }
+    })
+  }
+};
+</script>