package/tmux: add upstream security fix for CVE-2020-27347

Fixes CVE-2020-27347: The function input_csi_dispatch_sgr_colon() in file
input.c contained a stack-based buffer-overflow that can be exploited by
terminal output.

For details, see:
https://www.openwall.com/lists/oss-security/2020/11/05/3



Signed-off-by: Peter Korsgaard <peter@korsgaard.com>