Decode ref schema doesn't allow_nonref

[Relequestual]

With draft-6, ref schema may be boolean, which means allow_nonref must be 1 to allow scalar json encode and decode.
Pull request incoming.

On our dev systems, I am currently unable to install JSON Schema AsType, as one test fails.

# {
        #   'properties' => {
        #     '$ref' => {
        #       'type' => 'string'
        #     }
        #   }
        # }
        # Reference {"\$ref" => 2} did not pass type constraint "Properties[$ref,String]"
        # "Properties[$ref,String]" is defined as: sub { package JSON::Schema::AsType::Draft4::Types; return 1 unless Object->check($_); return $type->check($_); }
        # {
        #   '$ref' => '#/definitions/bool',
        #   'definitions' => {
        #     'bool' => bless( do{\(my $o = 1)}, 'JSON::PP::Boolean' )
        #   }
        # }
        # {
        #   '$ref' => '#/definitions/bool',
        #   'definitions' => {
        #     'bool' => bless( do{\(my $o = 0)}, 'JSON::PP::Boolean' )
        #   }
        # }
        # Child ($ref to boolean schema false) exited without calling finalize()
    
    #   Failed test '$ref to boolean schema false'
    #   at /usr/local/share/perl/5.18.2/Test/Builder.pm line 266.
hash- or arrayref expected (not a simple scalar, use allow_nonref to allow this) at /.../perl5/lib/perl5/JSON.pm line 154.
    # Child (t/json-schema-test-suite/tests/draft6/ref.json) exited without calling finalize()

#   Failed test 't/json-schema-test-suite/tests/draft6/ref.json'

It's strange that this problem isn't picked up by TravisCI running tests. I'm not sure why this is the case.

The only think I thought MIGHT be an issue is the notice at https://metacpan.org/changes/release/MAKAMAKA/JSON-2.90 for JSON 2.9, as I do have JSON::XS installed, but I still can't make the link.
My module versions are as follows:

# Versions for all modules listed in MYMETA.json (including optional ones):
# 
# === Configure Requires ===
# 
#     Module              Want Have
#     ------------------- ---- ----
#     ExtUtils::MakeMaker  any 7.22
# 
# === Build Requires ===
# 
#     Module              Want Have
#     ------------------- ---- ----
#     ExtUtils::MakeMaker  any 7.22
# 
# === Test Requires ===
# 
#     Module               Want     Have
#     ------------------- ----- --------
#     Exporter              any     5.68
#     ExtUtils::MakeMaker   any     7.22
#     File::Spec            any     3.40
#     IO::Handle            any     1.34
#     IPC::Open3            any     1.13
#     Path::Tiny          0.062    0.104
#     Test::Deep            any    0.114
#     Test::Exception       any     0.32
#     Test::More            any 1.001014
#     lib                   any     0.63
#     parent                any    0.225
# 
# === Test Recommends ===
# 
#     Module         Want     Have
#     ---------- -------- --------
#     CPAN::Meta 2.120900 2.150005
# 
# === Runtime Requires ===
# 
#     Module                  Want     Have
#     ---------------------- ----- --------
#     Class::Load              any     0.20
#     Clone                    any     0.36
#     JSON                     any     2.90
#     LWP::Simple              any     6.13
#     List::AllUtils           any     0.14
#     List::MoreUtils          any     0.33
#     List::Util               any     1.47
#     Moose                    any   2.1005
#     Moose::Role              any   2.1005
#     Moose::Util              any   2.1005
#     MooseX::ClassAttribute   any     0.29
#     MooseX::MungeHas         any    0.007
#     Path::Tiny             0.062    0.104
#     Scalar::Util             any     1.47
#     Type::Library            any 1.000005
#     Type::Tiny               any 1.000005
#     Type::Tiny::Class        any 1.000005
#     Type::Utils              any 1.000005
#     Types::Standard          any 1.000005
#     URI                      any     1.60
#     strict                   any     1.07
#     warnings                 any     1.18