Fixed GitHub link generation on Windows (resolves #318)

Author: kripod

lib/github.js

@@ -18,10 +18,14 @@ function getFileRoot(file) {
 module.exports = function (comment) {
   var root = getFileRoot(comment.context.file);
   var urlPrefix = getGithubURLPrefix(root);
+  var fileRelativePath = comment.context.file.replace(root + path.sep, '')
+    .split(path.sep)
+    .join('/');
+
   if (urlPrefix) {
-    comment.context.path = comment.context.file.replace(root + '/', '');
+    comment.context.path = fileRelativePath;
     comment.context.github = urlPrefix +
-      comment.context.file.replace(root + '/', '') +
+      fileRelativePath +
       '#L' + comment.context.loc.start.line + '-' +
       'L' + comment.context.loc.end.line;
   }