Update postmark.js to v2.2.5 to benefit of the /docs 30 Mo removed

[j1348]

This is related to this issue https://github.com/wildbit/postmark.js/issues/48

[killmenot]

It's not needed. https://github.com/killmenot/nodemailer-postmark-transport/blob/6d6a2a7715accec5c6e8266ebcd552996be157ff/package.json#L49 Once you install nodemailer-postmark-transport it loads latest postmark version bases on semver. ^2.2.3 means >= 2.0.0 < 3.0.0