.close() build.ninja in ninja generator

Appears to fix EOF corruption in build.ninja that appeared when
upgrading from python 2.6 to python 2.7.6 on XP hosts.

R=thakis@chromium.org, maruel@chomium.org

Review URL: https://codereview.chromium.org/75773002

git-svn-id: http://gyp.googlecode.com/svn/trunk@1792 78cadc50-ecff-11dd-a971-7dbc132099af