Add DOTNET_ROOT (#12)

* Add DOTNET_ROOT

* Correct path

* DOTNET_ROOT should point at root, not versioned folder

lib/installer.js

@@ -72,6 +72,8 @@ class DotnetCoreInstaller {
             else {
                 console.log('Using cached tool');
             }
+            // Need to set this so that .NET Core global tools find the right locations.
+            core.exportVariable('DOTNET_ROOT', path.join(toolPath, '../..'));
             // Prepend the tools path. instructs the agent to prepend for future tasks
             core.addPath(toolPath);
         });