UpdateBuildNumberOnlyMaster.ps1

if ($env:APPVEYOR_REPO_BRANCH -ne "master") {

  $headers = @{
    "Authorization" = "Bearer $env:API_TOKEN"
    "Content-type" = "application/json"
  }

  $apiURL = "https://ci.appveyor.com/api/projects/$env:APPVEYOR_ACCOUNT_NAME/$env:APPVEYOR_PROJECT_SLUG"
  $s = Invoke-RestMethod -Uri "https://ci.appveyor.com/api/projects/$env:APPVEYOR_ACCOUNT_NAME/$env:APPVEYOR_PROJECT_SLUG/settings" -Headers $headers  -Method Get
  $s.settings.nextBuildNumber = $s.settings.nextBuildNumber - 1
  Invoke-RestMethod -Uri 'https://ci.appveyor.com/api/projects' -Headers $headers  -Body ($s.settings | ConvertTo-Json -Depth 10) -Method Put

  $history = Invoke-RestMethod -Uri "$apiURL/history?recordsNumber=2" -Headers $headers  -Method Get
  if (($history.builds.Count -eq 2) -and ($($history.builds[1].branch) -eq 'master')) {
  Update-AppveyorBuild -Version "$($history.builds[1].version).$((New-Guid).ToString().Substring(0, 8))"
  }
  else {
  Update-AppveyorBuild -Version "$env:APPVEYOR_BUILD_VERSION.$((New-Guid).ToString().Substring(0, 8))"
  }

}