ignition-sensors6: revision bump rebuild for protobuf

Author: scpeters

Formula/ignition-sensors6.rb

@@ -4,7 +4,7 @@ class IgnitionSensors6 < Formula
   url "https://osrf-distributions.s3.amazonaws.com/ign-sensors/releases/ignition-sensors6-6.8.0.tar.bz2"
   sha256 "4bd5cd637dc624fe8d2a5244b3282ed74558c0fd50e040ba4770c312fcb8c1f5"
   license "Apache-2.0"
-  revision 17
+  revision 18
 
   head "https://github.com/gazebosim/gz-sensors.git", branch: "ign-sensors6"