Easter Date Goodie

**What does your Instant Answer do?**
Display Easter date and Passover date.

**What problem does your Instant Answer solve (Why is it better than organic links)?**
No need to view the web sites.

**What is the data source for your Instant Answer? (Provide a link if possible)**
Date::Passover, Date::Easter

**Why did you choose this data source?**
The modules are well-tested and provide answers for the years from 1900 to 2099.

**Are there any other alternative (better) data sources?**
It's possible to calculate the dates algorithmically for any year, but the CPAN modules already solve this task.

**What are some example queries that trigger this Instant Answer?**
easter 2015, passover 2015

**Which communities will this Instant Answer be especially useful for? (gamers, book lovers, etc)**
Jews, Catholics, and Orthodox Church believers.

**Is this Instant Answer connected to a DuckDuckHack [Instant Answer idea](https://duck.co/ideas)?**
No.

**Which existing Instant Answers will this one supercede/overlap with?**
None.

**Are you having any problems? Do you need our help with anything?**
None.

**What does the Instant Answer look like? (Provide a screenshot for new or updated Instant Answers)**
![easter_date](https://cloud.githubusercontent.com/assets/9570467/5576752/5c8d4fc4-8ffa-11e4-882b-61042b4c384f.png)


## Checklist
Please place an 'X' where appropriate.

```
[X] Added metadata and attribution information (https://duck.co/duckduckhack/metadata)
[X] Wrote test file and added to t/ directory (https://duck.co/duckduckhack/goodie_tests)
[X] Verified that instant answer adheres to design guidelines (https://duck.co/duckduckhack/design_styleguide)
[X] Verified that instant answer adheres to code styleguide (https://duck.co/duckduckhack/code_styleguide)
[] Tested cross-browser compatibility

    Please let us know which browsers/devices you've tested on:
    - Windows 8
        [] Google Chrome
        [X] Firefox
        [] Opera
        [] IE 10

    - Windows 7
        [] Google Chrome
        [] Firefox
        [] Opera
        [] IE 8
        [] IE 9
        [] IE 10

    - Windows XP
        [] IE 7
        [] IE 8

    - Mac OSX
        [] Google Chrome
        [] Firefox
        [] Opera
        [] Safari

    - iOS (iPhone)
        [] Safari Mobile
        [] Google Chrome
        [] Opera

    - iOS (iPad)
        [] Safari Mobile
        [] Google Chrome
        [] Opera

    - Android
        [] Firefox
        [] Native Browser
        [] Google Chrome
        [] Opera
```