[minor] undeclared recommended deps

[kentfredric]

{   "prereqs" : {
      "configure" : {
         "requires" : {
            "ExtUtils::MakeMaker" : "6.30"
         }
      },
      "develop" : {
         "requires" : {
            "Test::Pod" : "1.41"
         }
      },
      "runtime" : {
         "recommends" : {
            "JSON" : "0"
         },
         "requires" : {
            "perl" : "v5.8.1"
         }
      }
   }

This listing doesn't accomodate most of the optional dependencies that should be recommendations:

1. JSON::MaybeXS for tests
2. Readonly.pm for runtime

I only noticed because I was comparing old meta with new meta and found

https://metacpan.org/diff/file?target=INGY/boolean-0.42/&source=INGY/boolean-0.32/#META.yml

 recommends:
-  Readonly: '0'
+  JSON: '0'

Which seems like a regression of some kind =)

Especially when seen side by side with

 use boolean -truth;
-my $HAVE_JSON = eval { require JSON };
+my $HAVE_JSON = eval { require JSON::MaybeXS };
 SKIP: {
     skip "JSON is missing", 3 unless $HAVE_JSON;
     eval{
-        my $json = JSON->new->convert_blessed();
+        my $json = JSON::MaybeXS->new->convert_blessed();