Processes tree node.
@param {node} ast
function(ast) {
      var lastChild = ast.last();
      if (lastChild.is('space')) {
        lastChild.content = trim(lastChild.content)
            .replace(/[ \t]+$/, '')
            .replace(/[\n]+/g, '\n');
      }

      ast.traverseByType('space', function(space) {
        space.content = trim(space.content);
      });
    }