make signature match source

Author: coke

doc/Type/Telemetry/Sampler.pod6

@@ -40,7 +40,7 @@ the same as C<Telemetry::Instrument::Usage>.
 
 =head2 method set-instruments
 
-  method set-instruments(Telemetry::Sampler:D @instruments --> self)
+  method set-instruments(Telemetry::Sampler:D @instruments --> Nil)
 
 Allows one to change the instruments on an existing C<Instrument::Sampler>
 object.  Generally only used by calling it on the C<$*SAMPLER> dynamic variable.