refactor: use strings.EqualFold

[linchizhen]

strings.EqualFold has no memory overhead and has better performance than strings.ToLower.

This is a performance test:

package bench

import (
	"strings"
	"testing"
)

func BenchmarkToLower(b *testing.B) {

	str1 := "Windows"
	str2 := "windows"

	for i := 0; i < b.N; i++ {
		if strings.ToLower(str1) == strings.ToLower(str2) {
		}
	}
}

func BenchmarkEqualFold(b *testing.B) {

	str1 := "Windows"
	str2 := "windows"

	for i := 0; i < b.N; i++ {
		if strings.EqualFold(str1, str2) {
		}
	}
}

The result:

goos: darwin
goarch: arm64
BenchmarkToLower-8      31404808                36.99 ns/op            8 B/op          1 allocs/op
BenchmarkEqualFold-8    194780793                5.989 ns/op           0 B/op          0 allocs/op
PASS