Avoid unnecessary error creating cache dir

Author: jneira

.azure/linux-stack.yml

@@ -84,7 +84,7 @@ jobs:
   #     stack test --stack-yaml $(YAML_FILE)
   #   displayName: Run Test
   - bash: |
-      mkdir .azure-cache
+      mkdir -p .azure-cache
       tar -czf .azure-cache/stack-root.tar.gz $STACK_ROOT
       tar -czf .azure-cache/stack-work.tar.gz .stack-work
     displayName: "Pack cache"

.azure/macos-stack.yml

@@ -81,7 +81,7 @@ jobs:
   #     stack test --stack-yaml $(YAML_FILE)
   #   displayName: Run Test
   - bash: |
-      mkdir .azure-cache
+      mkdir -p .azure-cache
       tar -czf .azure-cache/stack-root.tar.gz $STACK_ROOT
       tar -czf .azure-cache/stack-work.tar.gz .stack-work
     displayName: "Pack cache"