typo in doc for Rational.norm

s/by/be/ looks like typo influenced by varname in example code

Author: arkiuat

doc/Type/Rational.rakudoc

@@ -118,7 +118,7 @@ language version, it's required for C<Rational> type to be normalized on
 creation.
 
 Returns a normalized Rational object, i.e. with positive denominator, and
-numerator and denominator coprime. The denominator can also by zero, but using
+numerator and denominator coprime. The denominator can also be zero, but using
 it in any operation or a conversion to string will result in an exception.
 
 =for code :solo