test: mark test-tick-processor flaky

PR-URL: https://github.com/nodejs/node/pull/4809
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Johan Bergström <bugs@bergstroem.nu>
Reviewed-By: James M Snell <jasnell@gmail.com>
Ref: https://github.com/nodejs/node/issues/4427

test/parallel/parallel.status

@@ -9,8 +9,10 @@ prefix parallel
 [$system==win32]
 test-debug-no-context                : PASS,FLAKY
 test-tls-ticket-cluster              : PASS,FLAKY
+test-tick-processor                  : PASS,FLAKY
 
 [$system==linux]
+test-tick-processor                  : PASS,FLAKY
 
 [$system==macos]