Replaced time-to-first-byte audit to server-response-time in lighthouse-config.js

[AndrewBarber]

What?

time-to-first-byte was replaced with server-response-time in lighthouse, which would cause this NPM script to fail.

Tickets / Documentation

• Lighthouse Proposal to replace time-to-first-byte
• Running Lighthouse NPM Script fails with `time-to-first-byte