Update dependency python-dotenv to ^0.15.0

[renovate]

This PR contains the following updates:

Package	Type	Update	Change
python-dotenv	dependencies	minor	^0.14.0 -> ^0.15.0

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Release Notes

theskumar/python-dotenv

v0.15.0

Compare Source

Added

• Add --export option to set to make it prepend the binding with export (#​270 by
  [@​jadutter]).

Changed

• Make set command create the .env file in the current directory if no .env file was
  found (#​270 by [@​jadutter]).

Fixed

• Fix potentially empty expanded value for duplicate key (#​260 by [@​bbc2]).
• Fix import error on Python 3.5.0 and 3.5.1 (#​267 by [@​gongqingkui]).
• Fix parsing of unquoted values containing several adjacent space or tab characters
  (#​277 by [@​bbc2], review by [@​x-yuri]).

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