perf tools: Add missing header to color.c

It uses isatty(), so needs unistd.h, include it.

Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: David Ahern <dsahern@gmail.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Wang Nan <wangnan0@huawei.com>
Link: http://lkml.kernel.org/n/tip-ivwuz8f68tb3sdcpguo9wmvx@git.kernel.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

tools/perf/util/color.c

@@ -3,6 +3,7 @@
 #include "config.h"
 #include "color.h"
 #include <math.h>
+#include <unistd.h>
 
 int perf_use_color_default = -1;