code: function lowerFirst(str) {
    if (!str) {
      return console.error('错误: lowerFirst 方法需要传入字符串类型的值');
    }
    return str.charAt(0).toLowerCase() + str.slice(1);
  }
docs: 首字母小写
  @param {string} str
  @return {string}
  
  @example
  Handlebars.compile('{{lowerFirst "abcDEF"}}')() // => "abcDEF"
  Handlebars.compile('{{lowerFirst "AbcDEF"}}')() // => "abcDEF"
  Handlebars.compile('{{lowerFirst "-AbcDEF"}}')() // => "-AbcDEF"
  Handlebars.compile('{{lowerFirst "A"}}')() // => "a"
  Handlebars.compile('{{lowerFirst ""}}')() // => ""