Replace call to deprecated ioutil.ReadAll with io.ReadAll

Starting from Go 1.16, ioutil.ReadAll simply calls io.ReadAll.

pkg/form.go

@@ -8,7 +8,7 @@ import (
 	"fmt"
 	"github.com/jackc/pgtype"
 	"html/template"
-	"io/ioutil"
+	"io"
 	"net/http"
 	"net/mail"
 	"net/url"
@@ -337,7 +337,7 @@ func (field *FileField) FillValue(r *http.Request) error {
 		return err
 	}
 	defer file.Close()
-	field.Content, err = ioutil.ReadAll(file)
+	field.Content, err = io.ReadAll(file)
 	if err != nil {
 		return err
 	}