write function types consistently with a space before fn keyword

Currently, the compiler (like @typeName) writes it `fn(...) Type` but
zig fmt writes it `fn (...) Type` (notice the space after `fn`).
This inconsistency is now resolved and function types are consistently
written the zig fmt way. Before this there were more `fn (...) Type`
occurrences than `fn(...) Type` already.

test/cases/compile_errors/invalid_array_elem_ty.zig

@@ -9,4 +9,4 @@ pub export fn entry() void {
 // target=native
 // backend=stage2
 //
-// :5:12: error: expected type 'type', found 'fn() type'
+// :5:12: error: expected type 'type', found 'fn () type'