Update go version for estimator

Created by: abeatrix

Detail in slack

Currently, our resource estimator in our docs is not able to load a locally hosted resource estimator through the ?dev=true URL Parama if it is built from the latest version of the resource-estimator repo

As mentioned in the thread by @slimsag :

on that page the script from Go 1.14 is being used, while your local dev server is using Go 1.18 and the generated WASM code expects the Go 1.18 script to be in use.

Also updating the go version from 1.16 to 1.18 in the resource-estimator repo

PR: https://github.com/sourcegraph/resource-estimator/pull/13/commits/d77befe579b44c09bb8c6577b616f0933240a9b7

Test plan

This is a doc update