In Go this is a shorthand for defining variables in bulk. Instead of having to write var in front of every variable declaration, you can use a var declaration block.
var ( a,b,c string = "this ", "is ","it " e,f,g int = 1, 2, 3 )
is the same as
var a,b,c string = "this ", "is ","it " var d,e,f int = 1, 2, 3
var () in your code example simply states that no variables were declared.
Refer to the official Go documentation for more information.