perf tools: Add trace/beauty/generated/ into .gitignore

No functionality changes.

Signed-off-by: Ravi Bangoria <ravi.bangoria@linux.vnet.ibm.com>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Link: http://lkml.kernel.org/r/20180130053053.13214-2-ravi.bangoria@linux.vnet.ibm.com


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