tmux.conf: lower escape-delay to 300 for NVim's :checkhealth

I am not sure what it does, so I am not using their adviced 10, but
instead 300 which is the maximum the :checkhealth doesn't complain
about.

conf/tmux.conf

@@ -37,3 +37,8 @@ set -g default-command "${SHELL}"
 
 # Resize window (not session) based on the smallest client viewing it
 setw -g aggressive-resize on
+
+# Lower escape-time to make Neovim's :checkhealth happy
+set -g escape-time 300
+# Or for tmux >= 2.6
+set -sg escape-time 300