Set exit status to return value of Inspec Runner

When invoking inspec using ```inspec exec PATH```, the script always
exits with a 0 status code. This pull request proposes to exit with the
same status code as the Inspec Runner. This behavior is consistent with
how testing platforms of this type typically work.

bin/inspec

@@ -87,7 +87,7 @@ class InspecCLI < Thor # rubocop:disable Metrics/ClassLength
 
     runner = Inspec::Runner.new(opts)
     runner.add_tests(tests)
-    runner.run
+    exit runner.run
   rescue RuntimeError => e
     puts e.message
   end