easylogging++: Generalize TERM rule for color-supporting terminals

With newer versions of tmux, such as version 3.4 packaged by Ubuntu
24.04, this is the default TERM variable value.

Instead of adding it specifically, extend the rule to look for
`-color` or `-256color` in TERM, as these can all be assumed to support
color.

external/easylogging++/easylogging++.cc

@@ -1246,9 +1246,9 @@ std::string OS::currentHost(void) {
 
 bool OS::termSupportsColor(void) {
   std::string term = getEnvironmentVariable("TERM", "");
-  return term == "xterm" || term == "xterm-color" || term == "xterm-256color"
-         || term == "screen" || term == "linux" || term == "cygwin"
-         || term == "screen-256color" || term == "screen.xterm-256color";
+  return term == "xterm" || term == "screen" || term == "linux" || term == "cygwin"
+         || term.find("-color") != std::string::npos
+         || term.find("-256color") != std::string::npos;
 }
 
 // DateTime