@reach/router behavior change from 1.2.1 to 1.3.4

Repro for reach/router#478

• Start with yarn && yarn start. You are now running with @reach/router 1.3.4.
• Click around on the links. You will see the log filling up with message about unmounting/mounting for every link you click (except when you go from /id/123 to /id/456 or vice versa).
• Stop the server
• yarn add @reach/router@1.2.1
• yarn start
• Click around on the links. You will only see unmounting/mounting messages when you go to/from the "Other component" link.