Bump version to 2.8.1 (opensearch-project#719)

Bump version to 2.8.1 per release process.

Issue:
opensearch-project#666

Signed-off-by: Kawika Avilla <kavilla414@gmail.com>
Signed-off-by: leanne.laceybyrne@eliatra.com <leanne.laceybyrne@eliatra.com>

package.json

@@ -1,6 +1,6 @@
 {
   "name": "opensearch-dashboards-functional-test",
-  "version": "2.8.0",
+  "version": "2.8.1",
   "description": "Maintains functional tests for OpenSearch Dashboards and Dashboards plugins",
   "main": "index.js",
   "scripts": {