Update dotenv requirement from 0.14.1 to 0.15.0

[dependabot[bot]]

Updates the requirements on dotenv to permit the latest version.

Release notes

Sourced from dotenv's releases.

0.15.0

Changed

• Undeprecate iter methods
• Library no longer has any dependencies

Added

• Support for variables with a . in their name
• Support \n in double-quoted lines
• Support for variable substitution

Changelog

Sourced from dotenv's changelog.

0.15.0 - 2019-10-21

Changed

• Undeprecate iter methods
• Library no longer has any dependencies

Added

• Support for variables with a . in their name
• Support \n in double-quoted lines
• Support for variable substitution

0.14.1 - 2019-05-14

Changed

• Deprecate iter methods.

0.14.0 - 2019-05-07

Changed

• Switched repo to use cargo workspaces.
• Renamed dotenv_codegen_impl to dotenv_codegen_implementation since we no longer own the original crate.
• Update code to 2018 edition

Commits

• 3840d4e update changelog for 0.15
• fa467c4 Merge pull request #30 from Eijebong/syn
• ab74c3b Update syn related dependencies to 1.0
• 6a400fe Merge pull request #26 from Swatinem/zero-deps
• 2c25991 Replace line-parsing RegEx by hand written parser
• c41d4c9 Support for variables with a literal dot in their name. (#25)
• 98b0ca9 Merge pull request #24 from hetoug/master
• e6ff659 Added test for \n. Added comments to warn of trailing blanks in tests
• 6f3e807 Add support for \n in doublequoted lines - needed by eg 'heroku config -s'
• 278580b Merge pull request #19 from dotenv-rs/add-changelog
• Additional commits viewable in compare view

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[wolf4ood]

@dependabot rebase