Fix broken link (#7378)

packages/next-server/server/render.tsx

@@ -295,7 +295,7 @@ export async function renderToHTML(
 
     if (dev && (props.router || props.Component)) {
       throw new Error(
-        `'router' and 'Component' can not be returned in getInitialProps from _app.js https://err.sh/zeit/next.js/cant-override-next-props.md`,
+        `'router' and 'Component' can not be returned in getInitialProps from _app.js https://err.sh/zeit/next.js/cant-override-next-props`,
       )
     }
   }

test/integration/no-override-next-props/test/index.test.js

@@ -22,6 +22,6 @@ describe('Dynamic require', () => {
 
   it('should show error when a Next prop is returned in _app.getInitialProps', async () => {
     const html = await renderViaHTTP(appPort, '/')
-    expect(html).toMatch(/https:\/\/err\.sh\/zeit\/next\.js\/cant-override-next-props\.md/)
+    expect(html).toMatch(/https:\/\/err\.sh\/zeit\/next\.js\/cant-override-next-props/)
   })
 })