Update pdf.js to v1.2

[jqnatividad]

Tons of fixes since the embedded v1.0.1207 early 2015

https://github.com/mozilla/pdf.js/releases

[jqnatividad]

bump. Make that v1.6.210 :)

[torfsen]

Note that v1.6.210 is a pre-release, the latest stable release is currently v1.5.188.

[arky]

Please kindly update PDF.js libraries to latest stable v2.5 (
https://github.com/mozilla/pdf.js/releases)

This is essential to render PDF documents with embedded fonts for southeast asian languages.