perf tools: Ignore 'perf timechart' output file

The default output file produced by the 'perf timechart' tool is called
output.svg, add it to .gitignore.

Signed-off-by: Ramkumar Ramachandra <artagnon@gmail.com>
Cc: Ingo Molnar <mingo@kernel.org>
Link: http://lkml.kernel.org/r/1380789636-4512-1-git-send-email-artagnon@gmail.com


Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>