Upgraded no-restricted-require in shared rule to error
Upgraded no-restricted-require in shared rule to error

- We should not require server or frontend files inside the shared libraries as these are intended to be required FROM the server and frontend components
- Now that we've resolved the two outstanding warnings, make this an error so we can't regress on this easily

e10/Ghost,TryGhost/Ghost,ErisDS/Ghost,ErisDS/Ghost,janvt/Ghost,TryGhost/Ghost,janvt/Ghost,TryGhost/Ghost,e10/Ghost,ErisDS/Ghost