jq: set mainProgram

Signed-off-by: Sefa Eyeoglu <[e-mail]>

pkgs/development/tools/jq/default.nix

···
     maintainers = with maintainers; [ raskin globin artturin ];
     platforms = platforms.unix;
     downloadPage = "https://stedolan.github.io/jq/download/";
+    mainProgram = "jq";
   };
 }