Update rollbar.js to latest (from 2.26.1 to 2.26.4)

[jeppeliisberg]

rollbar.js is added to my JS bundle by this gem, but it's not updated to the latest version.

[linear]

SDK-361 Update rollbar.js to latest (from 2.26.1 to 2.26.4)

[dkniffin]

I'm also seeing this warning in Rollbar

@waltjones can we get this resolved soon?

[shadoath]

Looks like Rollbar is now v3.1.0 is this gem planning to keep up with that?