evaluate upgrading to pyppeteer 1.x

[bollwyvl]

Elevator pitch

Raise the pin on pyppeteer to >=1,<1.1 from '==0.2.6'.

Motivation

A few 1.x releases have now gone out, and some time has elapsed to shake down any additional bugs. While a 1.x doesn't really mean anything, it seems like giving a package the benefit of the doubt that this will be a more stable API seems fair.

Especially if a major rev of nbconvert is on the horizon to support major revs of heavyweights like mistune (#1685) and mathjax (#1706), it would be good to get this one updated as well.

Additional context

Among the important things: at least its provisioning is no longer insecure-by-default, and requires up-to-date certificates. Its default chromium is still 588429, with claimed compatibility with puppeteer v1.6.0... but those haven't been updated in a long time. No telling what state it's actually in.