This latest update (1 June 2018, still current 4 June) to the FCO's travel advice for Turkey says:

"[P]residential and parliamentary elections will take place on 24 June 2018; this may result in rallies and demonstrations around the country; you should avoid large gatherings and follow the advice of the local authorities"

There's much more travel advice re Turkey on that FCO page, which you should look at if planning to visit there this summer.