win,msi: mark INSTALLDIR property as secure

Allows INSTALLDIR to be passed to the server MSIExec process during
installation.

PR-URL: https://github.com/nodejs/node/pull/8795
Fixes: https://github.com/nodejs/node/issues/6057
Reviewed-By: Benjamin Gruenbaum <benjamingr@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>

tools/msvs/msi/product.wxs

@@ -46,7 +46,7 @@
     <Property Id="ApplicationFolderName" Value="nodejs"/>
     <Property Id="WIXUI_INSTALLDIR" Value="INSTALLDIR"/>
 
-    <Property Id="INSTALLDIR">
+    <Property Id="INSTALLDIR" Secure="yes">
       <RegistrySearch Id="InstallPathRegistry"
                       Type="raw"
                       Root="HKLM"