Merge pull request #1636 from pofl/patch-1

Update godoc link in README to /v4

Author: lammel

README.md

@@ -1,7 +1,7 @@
 <a href="https://echo.labstack.com"><img height="80" src="https://cdn.labstack.com/images/echo-logo.svg"></a>
 
 [![Sourcegraph](https://sourcegraph.com/github.com/labstack/echo/-/badge.svg?style=flat-square)](https://sourcegraph.com/github.com/labstack/echo?badge)
-[![GoDoc](http://img.shields.io/badge/go-documentation-blue.svg?style=flat-square)](http://godoc.org/github.com/labstack/echo)
+[![GoDoc](http://img.shields.io/badge/go-documentation-blue.svg?style=flat-square)](https://pkg.go.dev/github.com/labstack/echo/v4)
 [![Go Report Card](https://goreportcard.com/badge/github.com/labstack/echo?style=flat-square)](https://goreportcard.com/report/github.com/labstack/echo)
 [![Build Status](http://img.shields.io/travis/labstack/echo.svg?style=flat-square)](https://travis-ci.org/labstack/echo)
 [![Codecov](https://img.shields.io/codecov/c/github/labstack/echo.svg?style=flat-square)](https://codecov.io/gh/labstack/echo)