Add weekdaysLetter to options on datePicker

Expected Behavior

Hi, I have problem with translation the datepicker, because I need to use key weekdaysLetter in Pickadate.DateOptions which is provided by orginal materializecss library, but here it seems to be not implemented.

Current Behavior

Its seems to work fine when app is on dev mode, npm compile it just fine, the problem shows when I try to run a ng build --prod, then it throws exception

Object literal may only specify known properties, and ‘weekdaysLetter’ does not exist in type ‘DateOptions’.

Possible Solution

Add weekdaysLetter?: string[]; to Pickadate.DateOptions (I did that locally and seems to work fine)

Steps to Reproduce (for bugs)

1. https://stackblitz.com/edit/ngx-materialize-etmuun

Context

Tying to compile the production version of app.

Your Environment

• Version used: 1.8.0-beta.0
• Angular version used: 5.2.0
• Browser Name and version: Opera/Chrome - Latest version
• Operating System and version (desktop or mobile): Desktop/Windows 10.0.16299.192

[LiadIdan]

@radoslawdabrowski the source of the issue is the types package for materialize, I submitted a PR to fix it.

[jfcere]

@LiadIdan update is on the way and btw thanks for your contribution on this issue!