Fix deprecated warning in dragonfly module

[KKIEEK]

/usr/local/lib/python3.7/site-packages/dragonfly/utils/oper_utils.py:30: UserWarning: cannot import name 'direct' from 'dragonfly.utils.direct_fortran' (/usr/local/lib/python3.7/site-packages/dragonfly/utils/direct_fortran/__init__.py)
Could not import Fortran direct library. Dragonfly can still be used, but might be slightly slower. To get rid of this warning, install a numpy compatible Fortran compiler (e.g. gfortran) and the python-dev package and reinstall Dragonfly.
  warn('%s\n%s'%(e, fortran_err_msg))