Remove the version number from `main.js`

[notlee]

The version of o-tracking is sent with each Spoor request.
As the version is set manually in main.js it tends to
get out of date.

Find out if the version is used and if not remove it.

[JakeChampion]

I spoke with the data team (https://financialtimes.slack.com/archives/C1WF81SR3/p1596034996208300) and we believe the version parameter is being used so we need to keep it.