fix reference to 'output_vehicles'

README.md

@@ -83,7 +83,7 @@ Inputs to Elara are MATSim format output files, eg:
 * **plans** = "./tests/test_fixtures/output_plans.xml"
 * **output_config_path** = "./tests/test_fixtures/output_config.xml"
 * **road pricing config** = "./tests/test_fixtures/roadpricing.xml"
-* **output_vehicles** = "./tests/test_fixtures/output_vehicles.xml"
+* **vehicles** = "./tests/test_fixtures/output_vehicles.xml"
 
 Depending on what outputs you require from elara, some of these inputs may not be required, but it is often convenient to have them all available as a default. In most cases these Elara inputs may be compressed using gzip (`file.xml.gz`).