fixed Method 'GET' already declared for route Error

[MomenNano]

I fixed the error addressed on this issue 61

Method 'GET' already declared for route '/'
caused by setting empty get path route fastify.get('/', <function>) after registering with prefix.
and websocket will register two paths <prefix> and <prefix/> and two handler. which causes this error.

p.s. This is my first PR ever! so if something is not right, I would be thankful if you could guide me :)

Checklist

• [✓ ] run npm run test and npm run benchmark
• [ ✓] tests and/or benchmarks are included
• documentation is changed or added
• [ ✓] commit message and code follows Code of conduct

[Eomm]

LGTM
as nit I would just reverse the logic (it would be more readable):

if (routeOptions.path === routeOptions.prefix) {
 return
}

[mcollina]

lgtm