chore(deps): update dependencies

[wass3r]

❤ THANKS FOR HELPING OUT :D

Proposed change

Updating dependencies. Particularly Slack. RTM has been non-functional for a little while 😱

Ref: https://github.com/nlopes/slack/issues/630

Types of changes

What types of changes is this pull request introducing to flottbot? Put an x in the boxes that apply

• Bugfix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)

Checklist

You can fill this out after creating your PR. Put an x in the boxes that apply

• I have added tests that prove my fix is effective or that my feature works
• I have added necessary documentation (if appropriate)

[coveralls]

Pull Request Test Coverage Report for Build 275

• 0 of 0 changed or added relevant lines in 0 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage remained the same at 37.945%

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Totals
Change from base Build 273:	0.0%
Covered Lines:	820
Relevant Lines:	2161

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💛 - Coveralls