refactor: move from io/ioutil to io and os packages (#1546)

The io/ioutil package has been deprecated as of Go 1.16, see
https://golang.org/doc/go1.16#ioutil. This commit replaces the existing
io/ioutil functions with their new definitions in io and os packages.

Signed-off-by: Eng Zer Jun <engzerjun@gmail.com>

core/data/data_test.go

@@ -2,13 +2,12 @@ package data
 
 import (
 	"fmt"
-	"io/ioutil"
 	"os"
 	"testing"
 )
 
 func TestMain(m *testing.M) {
-	dbFile, err := ioutil.TempFile(os.TempDir(), "owncast-test-db.db")
+	dbFile, err := os.CreateTemp(os.TempDir(), "owncast-test-db.db")
 	if err != nil {
 		panic(err)
 	}