benchmark: don't lint autogenerated modules

PR-URL: nodejs#10756
Reviewed-By: Rich Trott <rtrott@gmail.com>
Reviewed-By: Teddy Katz <teddy.katz@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Gibson Fahnestock <gibfahn@gmail.com>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>

.eslintignore

@@ -6,3 +6,4 @@ test/disabled
 test/tmp*/
 tools/eslint
 node_modules
+benchmark/tmp/