add golangci badge, and fix some lint issues found by the tool

README.md

@@ -1,5 +1,6 @@
 [![GoDoc](https://godoc.org/github.com/alexflint/go-arg?status.svg)](https://godoc.org/github.com/alexflint/go-arg)
 [![Build Status](https://travis-ci.org/alexflint/go-arg.svg?branch=master)](https://travis-ci.org/alexflint/go-arg)
+[![GolangCI](https://golangci.com/badges/github.com/alexflint/go-arg.svg)](https://golangci.com)
 [![Coverage Status](https://coveralls.io/repos/alexflint/go-arg/badge.svg?branch=master&service=github)](https://coveralls.io/github/alexflint/go-arg?branch=master)
 [![Report Card](https://goreportcard.com/badge/github.com/alexflint/go-arg)](https://goreportcard.com/badge/github.com/alexflint/go-arg)
 

parse_test.go

@@ -458,14 +458,14 @@ func TestHelpFlag(t *testing.T) {
 func TestPanicOnNonPointer(t *testing.T) {
 	var args struct{}
 	assert.Panics(t, func() {
-		parse("", args)
+		_ = parse("", args)
 	})
 }
 
 func TestPanicOnNonStruct(t *testing.T) {
 	var args string
 	assert.Panics(t, func() {
-		parse("", &args)
+		_ = parse("", &args)
 	})
 }
 

test/some-program/main.go

@@ -7,4 +7,5 @@ func main() {
 		Test string
 	}
 	arg.MustParse(&args)
+	_ = args.Test
 }

usage_test.go

@@ -2,14 +2,14 @@ package arg
 
 import (
 	"bytes"
+	"errors"
+	"fmt"
 	"os"
+	"strings"
 	"testing"
 
 	"github.com/stretchr/testify/assert"
 	"github.com/stretchr/testify/require"
-	"strings"
-	"fmt"
-	"errors"
 )
 
 type NameDotName struct {
@@ -89,15 +89,11 @@ Options:
 type MyEnum int
 
 func (n *MyEnum) UnmarshalText(b []byte) error {
-	b = []byte("Hello")
 	return nil
 }
 
-func (n *MyEnum) MarshalText() (text []byte, err error) {
-	s := "There was a problem"
-	text = []byte(s)
-	err = errors.New(s)
-	return
+func (n *MyEnum) MarshalText() ([]byte, error) {
+	return nil, errors.New("There was a problem")
 }
 
 func TestUsageError(t *testing.T) {