Replace deprecated ioutil pkg with os & io

As of Go 1.16, the same functionality is now provided by package io or
package os, and those implementations should be preferred in new code.

So replacing all usage of ioutil pkg with io & os.

source/github/github.go

@@ -3,15 +3,15 @@ package github
 import (
 	"context"
 	"fmt"
-	"golang.org/x/oauth2"
 	"io"
-	"io/ioutil"
 	"net/http"
 	nurl "net/url"
 	"os"
 	"path"
 	"strings"
 
+	"golang.org/x/oauth2"
+
 	"github.com/golang-migrate/migrate/v4/source"
 	"github.com/google/go-github/v39/github"
 )
@@ -194,7 +194,7 @@ func (g *Github) ReadUp(version uint) (r io.ReadCloser, identifier string, err e
 			if err != nil {
 				return nil, "", err
 			}
-			return ioutil.NopCloser(strings.NewReader(r)), m.Identifier, nil
+			return io.NopCloser(strings.NewReader(r)), m.Identifier, nil
 		}
 	}
 	return nil, "", &os.PathError{Op: fmt.Sprintf("read version %v", version), Path: g.config.Path, Err: os.ErrNotExist}
@@ -220,7 +220,7 @@ func (g *Github) ReadDown(version uint) (r io.ReadCloser, identifier string, err
 			if err != nil {
 				return nil, "", err
 			}
-			return ioutil.NopCloser(strings.NewReader(r)), m.Identifier, nil
+			return io.NopCloser(strings.NewReader(r)), m.Identifier, nil
 		}
 	}
 	return nil, "", &os.PathError{Op: fmt.Sprintf("read version %v", version), Path: g.config.Path, Err: os.ErrNotExist}

source/github/github_test.go

@@ -3,7 +3,7 @@ package github
 import (
 	"bytes"
 	"fmt"
-	"io/ioutil"
+	"os"
 	"testing"
 
 	st "github.com/golang-migrate/migrate/v4/source/testing"
@@ -13,7 +13,7 @@ import (
 var GithubTestSecret = "" // username:token
 
 func init() {
-	secrets, err := ioutil.ReadFile(".github_test_secrets")
+	secrets, err := os.ReadFile(".github_test_secrets")
 	if err == nil {
 		GithubTestSecret = string(bytes.TrimSpace(secrets)[:])
 	}