fix panic if hooks are not passed

[nikpivkin]

Fixes:

 go run .
panic: runtime error: invalid memory address or nil pointer dereference
[signal SIGSEGV: segmentation violation code=0x2 addr=0x8 pc=0x100a26f90]

goroutine 1 [running]:
github.com/sosedoff/gitkit.(*HookScripts).setupInDir(0x0, {0x1400009a5a0?, 0x140000b8ea0?})
        /Users/nikita/go/pkg/mod/github.com/sosedoff/gitkit@v0.4.0/config.go:31 +0xb0
github.com/sosedoff/gitkit.(*Config).setupHooks(0x140000f0180)
        /Users/nikita/go/pkg/mod/github.com/sosedoff/gitkit@v0.4.0/config.go:95 +0xec
github.com/sosedoff/gitkit.(*Config).Setup(0x140000f0180)
        /Users/nikita/go/pkg/mod/github.com/sosedoff/gitkit@v0.4.0/config.go:76 +0x58
github.com/sosedoff/gitkit.(*Server).Setup(...)
        /Users/nikita/go/pkg/mod/github.com/sosedoff/gitkit@v0.4.0/http.go:224
main.main()
        /Users/nikita/projects/gitkit-test/main.go:7 +0x330
exit status 2

Code:

package main

import "github.com/sosedoff/gitkit"

func main() {
	server := gitkit.New(gitkit.Config{AutoHooks: true, Dir: "test"})
	server.Setup()
}