use au_GalleryUrl if provided when checking package existence

closes #95

AU/Public/Update-Package.ps1

@@ -223,7 +223,8 @@ function Update-Package {
         $script:is_forced = $false
         if ([AUVersion] $Latest.Version -gt [AUVersion] $Latest.NuspecVersion) {
             if (!($NoCheckChocoVersion -or $Force)) {
-                $choco_url = "https://chocolatey.org/packages/{0}/{1}" -f $global:Latest.PackageName, $package.RemoteVersion
+                if ( !$au_GalleryUrl ) { $au_GalleryUrl = 'https://chocolatey.org' } 
+                $choco_url = "$au_GalleryUrl/packages/{0}/{1}" -f $global:Latest.PackageName, $package.RemoteVersion
                 try {
                     request $choco_url $Timeout | out-null
                     "New version is available but it already exists in the Chocolatey community feed (disable using `$NoCheckChocoVersion`):`n  $choco_url" | result

CHANGELOG.md

@@ -1,7 +1,9 @@
 # AU Project Changelog
 
 ## Next
-- `Update-Package`: Now you can pass HTTP/HTTPS headers to `$Latest.Options.Headers` to avoid `Unauthorized` errors while checking URLs.
+- `Update-Package`: 
+  - Now you can pass HTTP/HTTPS headers to `$Latest.Options.Headers` to avoid `Unauthorized` errors while checking URLs.
+  - Package Gallery URL is no longer hard-coded but taken from the `$au_GalleryUrl` if it exists ([#95](https://github.com/majkinetor/au/issues/95))
 - `Update-AUPackages`: Added `NoCheckChocoVersion` option.
 - Plugins:
   - `Git`: Added `Branch` parameter to specify a branch name

README.md

@@ -277,6 +277,8 @@ This is the same as if you added the parameters to `update` function inside the
 
 however, its way easier to setup global variable with manual intervention on multiple packages.
 
+There is also a special variable `$au_GalleryUrl` using which you can change the URL that is used to check if package is already pushed. It defaults to https://chocolatey.org and you can change it if you need to this option for 3rd party or internal package repositories. 
+
 ### Reusing the AU updater with metapackages
 
 Metapackages can reuse an AU updater of its dependency by the following way: