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.

cmd/mockery.go

@@ -3,15 +3,14 @@ package cmd
 import (
 	"context"
 	"fmt"
-	"io/ioutil"
 	"os"
 	"path/filepath"
 	"regexp"
 	"runtime/pprof"
 	"strings"
 	"time"
 
-	homedir "github.com/mitchellh/go-homedir"
+	"github.com/mitchellh/go-homedir"
 	"github.com/pkg/errors"
 	"github.com/rs/zerolog"
 	"github.com/rs/zerolog/log"
@@ -99,7 +98,7 @@ func printStackTrace(e error) {
 // Execute executes the cobra CLI workflow
 func Execute() {
 	if err := NewRootCmd().Execute(); err != nil {
-		//printStackTrace(err)
+		// printStackTrace(err)
 		os.Exit(1)
 	}
 }
@@ -247,7 +246,7 @@ func (r *RootApp) Run() error {
 
 	var boilerplate string
 	if r.Config.BoilerplateFile != "" {
-		data, err := ioutil.ReadFile(r.Config.BoilerplateFile)
+		data, err := os.ReadFile(r.Config.BoilerplateFile)
 		if err != nil {
 			log.Fatal().Msgf("Failed to read boilerplate file %s: %v", r.Config.BoilerplateFile, err)
 		}

pkg/generator_test.go

@@ -5,7 +5,7 @@ import (
 	"context"
 	"go/format"
 	"io"
-	"io/ioutil"
+	"os"
 	"path/filepath"
 	"strings"
 	"testing"
@@ -1359,15 +1359,15 @@ func NewRequesterReturnElided(t mockConstructorTestingTNewRequesterReturnElided)
 }
 
 func (s *GeneratorSuite) TestGeneratorVariadicArgs() {
-	expectedBytes, err := ioutil.ReadFile(getMocksPath("RequesterVariadic.go"))
+	expectedBytes, err := os.ReadFile(getMocksPath("RequesterVariadic.go"))
 	s.NoError(err)
 	expected := string(expectedBytes)
 	expected = expected[strings.Index(expected, "// RequesterVariadic is"):]
 	s.checkGeneration("requester_variadic.go", "RequesterVariadic", false, "", expected)
 }
 
 func (s *GeneratorSuite) TestGeneratorVariadicArgsAsOneArg() {
-	expectedBytes, err := ioutil.ReadFile(getMocksPath("RequesterVariadicOneArgument.go"))
+	expectedBytes, err := os.ReadFile(getMocksPath("RequesterVariadicOneArgument.go"))
 	s.NoError(err)
 	expected := string(expectedBytes)
 	expected = expected[strings.Index(expected, "// RequesterVariadicOneArgument is"):]

pkg/parse.go

@@ -5,7 +5,7 @@ import (
 	"fmt"
 	"go/ast"
 	"go/types"
-	"io/ioutil"
+	"os"
 	"path/filepath"
 	"sort"
 	"strings"
@@ -73,7 +73,7 @@ func (p *Parser) Parse(ctx context.Context, path string) error {
 
 	dir := filepath.Dir(path)
 
-	files, err := ioutil.ReadDir(dir)
+	files, err := os.ReadDir(dir)
 	if err != nil {
 		return err
 	}

pkg/walker.go

@@ -4,7 +4,6 @@ import (
 	"context"
 	"fmt"
 	"io"
-	"io/ioutil"
 	"os"
 	"path/filepath"
 	"regexp"
@@ -70,7 +69,7 @@ func (w *Walker) doWalk(ctx context.Context, p *Parser, dir string, visitor Walk
 	log := zerolog.Ctx(ctx)
 	ctx = log.WithContext(ctx)
 
-	files, err := ioutil.ReadDir(dir)
+	files, err := os.ReadDir(dir)
 	if err != nil {
 		return
 	}