.byebug_history included in default Rails5 setup (https://github.com/rails/rails/blob/master/railties/lib/rails/generators/rails/app/templates/gitignore)
@@ -33,3 +33,6 @@ bower.json
# Ignore pow environment settings
.powenv
+
+# Ignore Byebug command history file.
+.byebug_history
pisaacs