update chart version number, correctly set NC app version number in Chart

CHANGELOG.md

+## [0.2.8] - 2021-06-14
+
+* Enable ONLYOFFICE "forcesave" feature by default
+
 ## [0.2.7] - 2021-04-21
 
 * Update ONLYOFFICE version to 6.2.2.21

Chart.yaml

+---
 apiVersion: v2
 description: |
   A helm chart for installing NextCloud and setting up ONLYOFFICE integration
 name: nextcloud-onlyoffice
-version: 0.2.7
-appVersion: NC-0.2.5-OO-6.2.2.21
+version: 0.2.8
+appVersion: NC-19.0.3-OO-6.2.2.21
 dependencies:
   - name: nextcloud
     version: 2.5.0