| Subject: | write_json does not handle encoding properly |
```
# test.t
use strict;
use warnings;
use utf8;
use File::JSON::Slurper 'write_json';
use Test::More;
my $ref = { a => 'こんにちは' };
eval { write_json("ref.json", $ref, 'euc-jp') };
ok !$@, "no exception";
done_testing;
```
```
Show quoted text
> prove test.t
test.t .. 1/?
# Failed test 'no exception'
# at test.t line 12.
# Looks like you failed 1 test of 1.
test.t .. Dubious, test returned 1 (wstat 256, 0x100)
Failed 1/1 subtests
Test Summary Report
-------------------
test.t (Wstat: 256 Tests: 1 Failed: 1)
Failed test: 1
Non-zero exit status: 1
Files=1, Tests=1, 0 wallclock secs ( 0.02 usr 0.00 sys + 0.05 cusr 0.00 csys = 0.07 CPU)
Result: FAIL
```
`JSON::MaybeXS::encode_json` equals `JSON::MaybeXS->new->utf8(1)->encode`,
so `my $json = encode_json($ref)` is already a UTF-8 encoded, binary string.
https://github.com/neilb/File-JSON-Slurper/blob/master/lib/File/JSON/Slurper.pm#L22