Fix typo.

ev.pod

@@ -601,7 +601,7 @@ overhead for the actual polling but can deliver many events at once.
 By setting a higher I<io collect interval> you allow libev to spend more
 time collecting I/O events, so you can handle more events per iteration,
 at the cost of increasing latency. Timeouts (both C<ev_periodic> and
-C<ev_timer>) will be not affected. Setting this to a non-null bvalue will
+C<ev_timer>) will be not affected. Setting this to a non-null value will
 introduce an additional C<ev_sleep ()> call into most loop iterations.
 
 Likewise, by setting a higher I<timeout collect interval> you allow libev