Buggy neg int dump in not dec style

[puzrin]

js-yaml/lib/js-yaml/type/int.js

Lines 159 to 164 in c62fd62

	represent: {
	binary: function (object) { return '0b' + object.toString(2); },
	octal: function (object) { return '0' + object.toString(8); },
	decimal: function (object) { return object.toString(10); },
	hexadecimal: function (object) { return '0x' + object.toString(16).toUpperCase(); }
	},

• now: -10 -> 0b-1010
• should be: -10 -> -0b1010

The same for octal & hex.

Reference: #398 (comment)