Log Message:
Update ruby-prawrn to 2.0.0.

1. Changes to supported Ruby versions
2. Changes to PrawnPDF's versioning policies
3. All decimals in PDF output are now rounded to a fixed precision of
   4 decimal places
4. Fixed text width calculation to prevent unnecessary soft hyphen
5. Fixed styled text width calculations when using TTF files
6. Fixed broken vertical alignment for center and bottom
7. Calling dash(0) now raises an error instead of generating a corrupt PDF
8. Vastly improved handling of encodings for PDF built in (AFM) fonts
9. Temporarily restored the Document#on_page_create method

Please refer http://prawnpdf.org/api-docs/2.0/file.CHANGELOG.html in datail.