tmux: bump to version 2.6

Add license file hash.

Cc: Yann E. MORIN <yann.morin.1998@free.fr>
Signed-off-by: Baruch Siach <baruch@tkos.co.il>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>

package/tmux/tmux.hash

@@ -1,2 +1,3 @@
 # Locally computed:
-sha256 ae135ec37c1bf6b7750a84e3a35e93d91033a806943e034521c8af51b12d95df  tmux-2.5.tar.gz
+sha256 b17cd170a94d7b58c0698752e1f4f263ab6dc47425230df7e53a6435cc7cd7e8  tmux-2.6.tar.gz
+sha256 94e2b1feb1202d3308cc7ab7ec42278d24f10562394bdf269f44649327c8198f  README

package/tmux/tmux.mk

@@ -4,7 +4,7 @@
 #
 ################################################################################
 
-TMUX_VERSION = 2.5
+TMUX_VERSION = 2.6
 TMUX_SITE = https://github.com/tmux/tmux/releases/download/$(TMUX_VERSION)
 TMUX_LICENSE = ISC
 TMUX_LICENSE_FILES = README