AtCalendar 设置最大最小日期，显示BUG

**问题描述**

如题所示，设置maxDate：5/7，minDate 5/1，月份切到5月份显示正确，当月份是4月份的时候，日期显示不可用，感觉是个BUG

**复现步骤**

**系统信息**

Taro CLI 2.0.1 environment info:
System:
OS: macOS 10.15.4
Shell: 5.7.1 - /bin/zsh
Binaries:
Node: 11.6.0 - ~/.nvm/versions/node/v11.6.0/bin/node
npm: 6.10.2 - ~/.nvm/versions/node/v11.6.0/bin/npm
npmPackages:
@tarojs/cli: 2.0.1 => 2.0.1
@tarojs/components: 2.0.1 => 2.0.1
@tarojs/components-qa: 2.0.1 => 2.0.1
@tarojs/mini-runner: 2.0.1 => 2.0.1
@tarojs/redux: 2.0.1 => 2.0.1
@tarojs/redux-h5: 2.0.1 => 2.0.1
@tarojs/router: 2.0.1 => 2.0.1
@tarojs/taro: 2.0.1 => 2.0.1
@tarojs/taro-alipay: 2.0.1 => 2.0.1
@tarojs/taro-h5: 2.0.1 => 2.0.1
@tarojs/taro-qq: 2.0.1 => 2.0.1
@tarojs/taro-quickapp: 2.0.1 => 2.0.1
@tarojs/taro-swan: 2.0.1 => 2.0.1
@tarojs/taro-tt: 2.0.1 => 2.0.1
@tarojs/taro-weapp: 2.0.1 => 2.0.1
@tarojs/webpack-runner: 2.0.1 => 2.0.1
eslint-config-taro: 2.0.1 => 2.0.1
eslint-plugin-taro: 2.0.1 => 2.0.1
nerv-devtools: ^1.5.6 => 1.5.6
nervjs: ^1.5.6 => 1.5.6
stylelint-config-taro-rn: 2.0.1 => 2.0.1
stylelint-taro-rn: 2.0.1 => 2.0.1
- Taro UI 版本 [e.g. v.2.3.4]