Merge pull request Polymer#5691 from eltociear/patch-3

Fix typo in disable-upgrade-mixin.js

Author: kevinpschaaf

lib/mixins/disable-upgrade-mixin.js

@@ -126,7 +126,7 @@ export const DisableUpgradeMixin = dedupingMixin((base) => {
      */
     attributeChangedCallback(name, old, value, namespace) {
       if (name == DISABLED_ATTR) {
-        // When disable-upgrade is removed, intialize properties and
+        // When disable-upgrade is removed, initialize properties and
         // provoke connectedCallback if the element is already connected.
         if (this.__isUpgradeDisabled && value == null) {
           super._initializeProperties();