docs: updates install links for 4.1.0 beta

scripts/trigger_windows_build.sh

@@ -5,5 +5,5 @@ _token=$1
 curl \
   -H "Content-Type: application/json" \
   -H "Authorization: Bearer ${_token}" \
-  -X POST -d '{ "accountName": "Torkeldegaard", "projectSlug": "grafana","branch": "v4.0.x","environmentVariables": {}}' \
+  -X POST -d '{ "accountName": "Torkeldegaard", "projectSlug": "grafana","branch": "master","environmentVariables": {}}' \
   https://ci.appveyor.com/api/builds