[black] Unpin python to check if it biulds correctly (not for py37!)

conda/black/meta.yaml

@@ -19,10 +19,10 @@ build:
 
 requirements:
   host:
-    - python >=3.6
+    - python
     - pip
   run:
-    - python >=3.6
+    - python
     - click >=6.5
     - attrs >=18.1.0
     - appdirs