[CPAN-Meta] fix string comparisons with $] to use numeric comparison instead

The fix follows Zefram's suggestion from
https://www.nntp.perl.org/group/perl.perl5.porters/2012/05/msg186846.html

> On older perls, however, $] had a numeric value that was built up using
> floating-point arithmetic, such as 5+0.006+0.000002.  This would not
> necessarily match the conversion of the complete value from string form
> [perl #72210].  You can work around that by explicitly stringifying
> $] (which produces a correct string) and having *that* numify (to a
> correctly-converted floating point value) for comparison.  I cultivate
> the habit of always stringifying $] to work around this, regardless of
> the threshold where the bug was fixed.  So I'd write
>
>     use if "$]" >= 5.014, warnings => "non_unicode";

Author: book

cpan/CPAN-Meta/lib/CPAN/Meta.pm

@@ -398,7 +398,7 @@ sub save {
   my ($self, $file, $options) = @_;
 
   my $version = $options->{version} || '2';
-  my $layer = $] ge '5.008001' ? ':utf8' : '';
+  my $layer = "$]" >= 5.008001 ? ':utf8' : '';
 
   if ( $version ge '2' ) {
     carp "'$file' should end in '.json'"