(GH-729) Update env after setting env vars for scripts

When setting environment variables, update the session's environment
variables so that those variables can be used immediately in the
currently running PowerShell script.

src/chocolatey.resources/helpers/functions/Set-EnvironmentVariable.ps1

@@ -42,4 +42,6 @@ function Set-EnvironmentVariable([string] $Name, [string] $Value, [System.Enviro
   }
 
   [Microsoft.Win32.Registry]::SetValue($keyHive + "\" + $registryKey, $Name, $Value, $registryType)
+
+  Update-SessionEnvironment
 }