Settings: Round `defaultVolume`'s getter value to the nearest integer

This fixes a bug related to the presentation of the `defaultVolume`
value in its respective label in the Settings view.

Since the value stored in the database and in the in-memory store
is a decimal number, it is subject to floating point arithmetic related
limitations.

Example (processed by the V8 engine):
0.28 * 100 = 28.000000000000004

src/renderer/components/player-settings/player-settings.js

@@ -67,7 +67,7 @@ export default Vue.extend({
     },
 
     defaultVolume: function () {
-      return parseFloat(this.$store.getters.getDefaultVolume) * 100
+      return Math.round(parseFloat(this.$store.getters.getDefaultVolume) * 100)
     },
 
     defaultPlayback: function () {