Update image location after move to the Microsoft Container Registry

azure-pipelines.yml

@@ -9,7 +9,7 @@ variables:
 resources:
   containers:
   - container: LinuxContainer
-    image: microsoft/dotnet-buildtools-prereqs:ubuntu-14.04-cross-0cd4667-20170319080304
+    image: mcr.microsoft.com/dotnet-buildtools/prereqs:ubuntu-14.04-cross-0cd4667-20170319080304
     options: --init # This ensures all the stray defunct processes are reaped.
 
 trigger: