fix bug: remove dupliated root path when using asset_img tag

[darkrasid]

solving #2123

• plugin img tag resolve root path twice

on lib/plugin/tag/asset_img.js

  args[i] = url.resolve(ctx.config.root, asset.path);  << first 

and on lib/plugin/tag/img.js

  function makeUrl(path) {
    if (path[0] === '#' || path.substring(0, 2) === '//') {
      return path;
    }

    var data = url.parse(path);

    if (data && data.protocol) {
      return path;
    }

    path = config.root + path;

    return path.replace(/\/{2,}/g, '/'); << second
  }

I think there is no reason to prefix root config twice.

[coveralls]

Coverage remained the same at 97.224% when pulling 407fed8 on darkrasid:fix_img_tag_bug into d40879b on hexojs:master.

[JLHwung]

Could you add some test case regarding to #2123? It will prevent any further regression, thank you.

[coveralls]

Coverage remained the same at 97.224% when pulling 39b700b on darkrasid:fix_img_tag_bug into d40879b on hexojs:master.

[darkrasid]

@JLHwung No problem. I add test case.

[coveralls]

Coverage remained the same at 97.224% when pulling 39b700b on darkrasid:fix_img_tag_bug into d40879b on hexojs:master.

[coveralls]

Coverage remained the same at 97.224% when pulling c14aba3 on darkrasid:fix_img_tag_bug into d40879b on hexojs:master.

[JLHwung]

Thank you so much for you contribution. Hexo can't be rock without contributors like you.