Fix warning

bin/tmx

@@ -23,7 +23,7 @@ else
     # Make sure we are not already in a tmux session
     if [[ -z "$TMUX" ]]; then
         # Kill defunct sessions first
-        old_sessions=$(tmux ls 2>/dev/null | egrep "^[0-9]{14}.*[0-9]+\)$" | cut -f 1 -d:)
+        old_sessions=$(tmux ls 2>/dev/null | grep -E "^[0-9]{14}.*[0-9]+\)$" | cut -f 1 -d:)
         for old_session_id in $old_sessions; do
             tmux kill-session -t $old_session_id
         done