fix(examples): fix examples of reflected XSS attack

[yoshiakis]

Changes proposed in this pull request:

• fix: missing apollo-server-express which is necessary

• fix: wrong endpoint

• docs: add URI for example 4 (@acao I think that is what you intended to do but you've forgot to do that, is that right? :))

[acao]

yes, my bad! i must have forgotten to push a last commit or two here.

[acao]

thanks @yoshiakis !