Fixed routerKey prop eslint warning

Eslint throws a warning to props that don't have a default value

- Added a default value to the routerKey prop.

Signed-off-by: Kenneth Fullbright <kennyneedsmilky@gmail.com>
Change-Id: I2d9d4abd0512eeadf27f8941a0f391979eb9a80a
diff --git a/src/components/AppHeader/AppHeader.vue b/src/components/AppHeader/AppHeader.vue
index aa5b024..84e4588 100644
--- a/src/components/AppHeader/AppHeader.vue
+++ b/src/components/AppHeader/AppHeader.vue
@@ -128,7 +128,10 @@
   },
   mixins: [BVToastMixin],
   props: {
-    routerKey: Number,
+    routerKey: {
+      type: Number,
+      default: 0,
+    },
   },
   data() {
     return {