avoid typo, change word slightly

Author: coke

doc/Type/Backtrace.pod6

@@ -38,7 +38,7 @@ Defined as:
 
 Returns a concise string representation of the backtrace, omitting
 routines marked as C<is hidden-from-backtrace>, and at the discretion of
-the implementor, also some routines from the setting.
+the implementation, also some routines from the setting.
 
     my $backtrace = Backtrace.new;
     say $backtrace.Str;