remove trailing whitespace

Author: coke

doc/Type/Promise.pod6

@@ -74,7 +74,7 @@ this method:
 Creates a new Promise that will be kept in C<$seconds> seconds, or later.
 
     my $proc = Proc::Async.new('perl6', '-e', 'sleep 10; warn "end"');
-    
+
     my $result = await Promise.anyof(
         my $promise = $proc.start,
         Promise.in(5).then: { note 'timeout'; $proc.kill }