(#201) Correcting uninstallation

Rather than make a direct call to msiexec, use the Chocolatey Helper Method, which should handle waiting on the MSI to complete the uninstallation, and then carry on with writing Chocolatey success message.

ChocolateyPackage/chocolateyUninstall.ps1

@@ -1,20 +1,23 @@
-$package = "ChocolateyGUI"
+$packageName = "ChocolateyGUI";
+$fileType = 'msi';
+$silentArgs = '/qr /norestart'
+$validExitCodes = @(0)
 
 try {
   	$packageGuid = Get-ChildItem HKLM:\SOFTWARE\Classes\Installer\Products |
     	Get-ItemProperty -Name 'ProductName' |
-    	? { $_.ProductName -like $package + "*"} |
+    	? { $_.ProductName -like $packageName + "*"} |
     	Select -ExpandProperty PSChildName -First 1
 
 	$properties = Get-ItemProperty HKLM:\SOFTWARE\Microsoft\Windows\CurrentVersion\Installer\UserData\S-1-5-18\Products\$packageGuid\InstallProperties
 
-	$pkg = $properties.LocalPackage
+	$file = $properties.LocalPackage
 
-	msiexec.exe /x $pkg /qr /norestart
+	Uninstall-ChocolateyPackage $packageName $fileType $silentArgs $file -validExitCodes $validExitCodes
 
 	Write-ChocolateySuccess $package
 }
 catch {
 	Write-ChocolateyFailure $package "$($_.Exception.Message)"
 	throw
-}
+}