Upgrade to mpdf 8.0.0

Merge pull request #29 from Julian-B90/master

convert tab to space, install mpdf 8

Fixes mpdf and PHP version number errors

Fixes #21

Typo in composer.json

Adds mpdf upper bound

1.0.2

Add mpdf upper bounf (fix #20)

Fixed typo

1.0.1

Fixes #9

First release

1.0.0

Added mPDF minimal version requirement to composer.json