Reduce the number of concurrent builds

makefile.shade

@@ -89,7 +89,7 @@ var buildTarget = "compile"
 
         foreach (var batch in batchedRepos)
         {
-            Parallel.ForEach(batch, repo =>
+            Parallel.ForEach(batch, new ParallelOptions { MaxDegreeOfParallelism = 2 }, repo =>
             {
                 var blockName = string.Format("Building {0}", repo);