Bumps the env version to es2017

[peterramsing]

What kind of change is this? (Bug Fix, Feature...)
infra

What is the current behavior (You can also link to an issue)
lints to es6

What is the new behavior this introduces (if any)
lints to es2017

Does this introduce any breaking changes?
No

Does the PR fulfill these requirements?

• [-] Tests for the changes have been added
• [-] Docs have been added or updated

Other Comments

[codecov]

Codecov Report

Merging #454 (eff4246) into master (49c96c8) will not change coverage.
The diff coverage is n/a.

@@            Coverage Diff            @@
##            master      #454   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files           20        20           
  Lines          776       776           
=========================================
  Hits           776       776           

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