Fix typo in document

This PR fix typo in document

docs/runtime_options.md

@@ -16,7 +16,7 @@ Housekeeping is the periodic actions cAdvisor takes. During these actions, cAdvi
 
 #### Dynamic Housekeeping
 
-Dynamic housekeeping intervals let cAdvisor very how often it gathers stats.
+Dynamic housekeeping intervals let cAdvisor vary how often it gathers stats.
 It does this depending on how active the container is. Turning this off
 provides predictable housekeeping intervals, but increases the resource usage
 of cAdvisor.