Remove tornado max version from nightly recipe (#7376)

Author: charlesbluca

continuous_integration/recipes/distributed/meta.yaml

@@ -42,7 +42,7 @@ requirements:
     - sortedcontainers !=2.0.0,!=2.0.1
     - tblib >=1.6.0
     - toolz >=0.10.0
-    - tornado >=6.0.3,<6.2
+    - tornado >=6.0.3
     - urllib3
     - zict >=0.1.3
   run_constrained: