Fix: Invalid parameter with single page number as string.

[Furkangunduz]

I just extend the add function from under the pdf merge. And create test by copying other tests. Now able to add by parameter as string.

[mojoaxel]

Thank you very much for your contribution!

• Please check again your indentation.
• run npm run standard
• Also I would move the regex-check to the end of the if-else chain because regex are quite "expensive".
• Could you maybe also implement the possibility to give plain numbers!?
  Something like this: add(inputFile, 3)

I'll try to merge as soon as I have access to a real computer (I'm on vacation).

[Furkangunduz]

Hello ,
I edited my code. I moved the regex end of the if-else chain , add new if else to check if parameter "pages" is number and add test for plain numbers.

it was a pleasure a helping. Have fun on your vacation.

[mojoaxel]

Thx! LGTM