Fix Dockerfile link in README

cc: @eilon
Merge pull request #8 from muojp/master

Add build of libuv for supporting Kestrel Web Server
Merge pull request #6 from ahmetalpbalkan/patch-1

Fix Dockerfile link in README (fixes #5)
Remove 1.0.0-alpha4

To fix the build break and continue maintaining docker
tags starting from beta1, removed 1.0.0-alpha4 dockerfile
and fixed readme.

Signed-off-by: Ahmet Alp Balkan <ahmetb@microsoft.com>
Merge pull request #15 from ahmetalpbalkan/remove-alpha4

Remove 1.0.0-alpha4
Merge pull request #1 from aspnet/master

Sync to upstream