Don't use interpolated strings for username and password

Its possible that usernames and passwords may contain special characters like $

plugins/communicators/winrm/scripts/elevated_shell.ps1.erb

@@ -1,6 +1,6 @@
 $command = "<%= options[:command] %>"
-$user = "<%= options[:username] %>"
-$password = "<%= options[:password] %>"
+$user = '<%= options[:username] %>'
+$password = '<%= options[:password] %>'
 
 $task_name = "WinRM_Elevated_Shell"
 $out_file = "$env:SystemRoot\Temp\WinRM_Elevated_Shell.log"