fix quoting for Windows compile

Author: rvagg

binding.gyp

@@ -5,7 +5,7 @@
       'sources': ['src/binding.cc'],
       'include_dirs': [
         '<!@(pg_config --includedir)',
-        '<!(node -e \'require("nan")\')'
+        '<!(node -e "require(\'nan\')")'
       ],
       'conditions' : [
         ['OS=="win"', {