Set version to beta1 for a release.

version.json

@@ -1,6 +1,6 @@
 {
   "$schema": "https://raw.githubusercontent.com/AArnott/Nerdbank.GitVersioning/master/src/NerdBank.GitVersioning/version.schema.json",
-  "version": "1.2.0.0",
+  "version": "1.2.0.0-beta1",
   "cloudBuild": {
     "buildNumber": {
       "enabled": true