Processes tree node.
@param {node} ast
function(ast) {
    let value = this.value;

    ast.traverseByType('number', function(number) {
      if (!value) {
        number.content = number.content.replace(/^0+(?=\.)/, '');
      } else if (number.content[0] === '.') {
        number.content = '0' + number.content;
      }
    });
  }