text: Title: No module named 'databricks' after installing koalas
  Body: I have installed koalas using conda install. 
  However when I try the following import, I get an ModuleNotFoundError.
  Can you help me to solve this issue?
  
  >>> import databricks.koalas as ks
  Traceback (most recent call last):
    File "<stdin>", line 1, in <module>
  ModuleNotFoundError: No module named 'databricks'