Pass brightray.gypi via parameters.

We need to make sure node.gyp can get variables in brightray.gypi, this
needs minimum modifications.

atom.gyp

@@ -30,9 +30,6 @@
       'app/atom_library_main.h',
     ],
   },
-  'includes': [
-    'vendor/brightray/brightray.gypi',
-  ],
   'targets': [
     {
       'target_name': '<(project_name)',

script/update

@@ -4,4 +4,4 @@ set -e
 
 cd "$(dirname "$0")/.."
 
-gyp --depth . atom.gyp
+gyp --depth . atom.gyp -I vendor/brightray/brightray.gypi