Update Windows version macros to Win 7

BUG=92941
Review URL: http://codereview.chromium.org/8004004

git-svn-id: http://src.chromium.org/svn/trunk/src/build@102735 4ff67af0-8c30-449e-8e8b-ad334ec8d88c

common.gypi

@@ -2211,8 +2211,8 @@
     ['OS=="win"', {
       'target_defaults': {
         'defines': [
-          '_WIN32_WINNT=0x0600',
-          'WINVER=0x0600',
+          '_WIN32_WINNT=0x0601',
+          'WINVER=0x0601',
           'WIN32',
           '_WINDOWS',
           'NOMINMAX',