should not change method to replaceState unless asPath is the same

[tangye1234]

original code in /lib/router/router.js

  urlIsNew (pathname, query) {
    return this.pathname !== pathname || !shallowEquals(query, this.query)
  }

the urlIsNew compare this.pathname to an argument pathname
the invokers:

    // If asked to change the current URL we should reload the current page
    // (not location.reload() but reload getInitialProps and other Next.js stuffs)
    // We also need to set the method = replaceState always
    // as this should not go into the history (That's how browsers work)
    if (!this.urlIsNew(asPathname, asQuery)) {
      method = 'replaceState'
    }

the parameter here is asPathname destructured from asPath

so here is a problem when we reuse a single page rendered in two asPaths

pages/a.js

<>
  <Link href='/a'><a>goto a</a></Link>
  <Link href='/a' as='/b'><a>goto b</a></Link>
</>

If we navigate to page /a, then click 'goto b', actually the history is replaced, not pushed.
It is expected that history could be correctly pushed and popped as long as the browser url is changed.

[dav-is]

Looks like there was a caching error in TravisCI. I cleared the cache and now the tests pass 🙌

[timneutkens]

Great PR 🙏