fix error with hash keys beginning with '-'

YAML::Tiny fails to parse a hash where the key beigns with
'-' (e.g. '-foo') with the error:
YAML::Tiny found illegal characters in plain scalar: 'family: 'Courier 10 Pitch'' at test-yaml.pl line 21.

Here's an example below, with a test program, the yaml file written by
the test program and the result of the script:

$ cat test-yaml.pl
use strict;
use warnings;
use YAML::Tiny;
use XXX;

my $data = {
          '-weight' => 'normal',
          '-overstrike' => 0,
          '-size' => -13,
          '-slant' => 'roman',
          '-underline' => 0,
          '-family' => 'Courier 10 Pitch'
        };

my $config_file= 'test.yml';

my $config_yaml = YAML::Tiny->new ( { font => $data } );

$config_yaml->write($config_file);

my $new_config = YAML::Tiny->read($config_file) ;
YYY $new_config;

devel$ cat test.yml
---
font:
  -family: 'Courier 10 Pitch'
  -overstrike: 0
  -size: -13
  -slant: roman
  -underline: 0
  -weight: normal

devel$ perl test-yaml.pl
YAML::Tiny found illegal characters in plain scalar: 'family: 'Courier 10 Pitch'' at test-yaml.pl line 21.

lib/YAML/Tiny.pm

@@ -528,7 +528,7 @@ sub _load_hash {
                 $hash->{$key} = undef;
                 return 1;
             }
-            if ( $lines->[0] =~ /^(\s*)-/ ) {
+            if ( $lines->[0] =~ /^(\s*)-(?:\s|$)/ ) {
                 $hash->{$key} = [];
                 $self->_load_array(
                     $hash->{$key}, [ @$indent, length($1) ], $lines

t/10_read.t

@@ -34,6 +34,12 @@ my %passes = (
         ],
         utf8 => 'author',
     },
+    'hash with key' => {
+        file => 'font-data.yml',
+        perl => [
+            { font => { -family => 'Courier 10 Pitch', -overstrike => 0 } }
+        ]
+    }
 );
 
 for my $key ( sort keys %passes ) {

t/data/font-data.yml

@@ -0,0 +1,4 @@
+---
+font:
+  -family: 'Courier 10 Pitch'
+  -overstrike: 0