Check if APPVEYOR_BUILD_VERSION set and use that as nupkg version

appveyor.yml

@@ -1,7 +1,7 @@
 environment:
   VisualStudioVersion: 11.0
 
-version: 37.0.0.CI{build}
+version: 37.0.0-CI{build}
 
 shallow_clone: true
 

build.ps1

@@ -3,7 +3,7 @@ param(
     [Parameter(Position = 0)] 
     [string] $Target = "nupkg",
     [Parameter(Position = 1)]
-    [string] $Version = "37.0.0-pre02",
+    [string] $Version = "37.0.0-pre01",
 	[Parameter(Position = 2)]
     [string] $AssemlyVersion = "37.0.0",
     [Parameter(Position = 3)]
@@ -14,6 +14,11 @@ $WorkingDir = split-path -parent $MyInvocation.MyCommand.Definition
 
 $CefSln = Join-Path $WorkingDir 'CefSharp3.sln'
 
+if (Test-Path Env:\APPVEYOR_BUILD_VERSION)
+{
+    $Version = Env:\APPVEYOR_BUILD_VERSION
+}
+
 # https://github.com/jbake/Powershell_scripts/blob/master/Invoke-BatchFile.ps1
 function Invoke-BatchFile 
 {