Update index.bs

Co-authored-by: Maksim Sadym <[email protected]>

Author: OrKoN

index.bs

@@ -1441,7 +1441,7 @@ To <dfn>update the event map</dfn>, given
 |session|, |requested event names|, |navigables|, and |enabled|:
 
 Note: The return value of this algorithm is a map between event names and
-contexts. When the events are being enabled, the contexts in the return value
+navigables. When the events are being enabled, the navigables in the return value
 are those for which the event are now enabled but were not previously. When
 events are disabled, the return value is always empty.