fix: tag-handle may include digits in directive

[mighty1231]

What does it fix?

normal tag directive - %TAG !taghandle! tag:yaml.org,2002:

test case %TAG !12345! tag:yaml.org,2002:

• currently js-yaml throw error during parsing tag directive
• expected it should not throw error

reference: c-tag-handle

• "c-tag-handle" may be "c-named-tag-handle"
• c-named-tag-handle ::= "!" ns-word-char + "!"
• ns-word-char defined as one of ns-dec-digit, ns-ascii-letter or "-"
• and finally ns-dec-digit is [0-9]

My references is from yaml 1.1, but these things have not been changed in yaml 1.2 spec