SyntaxWarning in `pretrainedmodels/models/dpn`

[shaharma93]

I get

 <python_path>site-packages/pretrainedmodels/models/dpn.py:255: SyntaxWarning: "is" with a literal. Did you mean "=="?
  if block_type is 'proj':

I get this warning in the following lines: 255, 258, 262
Is there a reason to use is and not ==? I think comparing strings with == is indeed more elegant..

[Fzz123]

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[shaharma93]

I opened a pull request
#236