Investigate trailing slashes

[cheapsteak]

https://www.apollographql.com/docs/resources/graphql-glossary

1 goal : have automated checkers use the same url as an editor would see

A link checker: https://www.drlinkcheck.com/account/subscriptions/1/projects/2/reports/broken?offset=1753&count=100

[trevorblades]

A couple of other issues following this:

• https://github.com/gatsbyjs/gatsby/issues/9207
• https://github.com/gatsbyjs/gatsby/issues/15317