Saving the modified user doc for Role Elevation from User to Author should propogate the change in role across active sessions

[Martii]

As per @sizzlemctwizzle comment from https://github.com/OpenUserJs/OpenUserJS.org/issues/1107#issuecomment-300274429 and https://github.com/OpenUserJs/OpenUserJS.org/issues/1107#issuecomment-300275368 :

... call the update method of libs/modifySessions.js to make sure the change is propagated in the session store.

This is followup for the perceived missing logic in that code section that was not there before the PR of #1108

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NOTES:

• Missing aReq object to call existing modifySessions.update e.g. not in top level function signature.
• RepoManager.loadScripts doesn't currently have aReq with a user in it on import scripts from GH (e.g. webhook won't be able to elevate using current modifySessions.update)