remove trailing whitespace

Author: coke

doc/Type/Signature.pod6

@@ -258,9 +258,9 @@ There are two other ways to declare a return type:
 
 C<of> is just the real name of the C<returns> keyword, and the
 prefix(C-like) form can be used too. Although all the ways are valid,
-the C<-->> form is preferred for several reasons: 
+the C<-->> form is preferred for several reasons:
 (1) it can handle constant values while the others can't;
-(2) for consistency, it is the only form accepted on this site; and 
+(2) for consistency, it is the only form accepted on this site; and
 (3) the C<returns> form is planned for future removal.
 
 The following illustrates how to write a signature returning a constant value: