Dependency Fixes

[djizco]

• Upgrade babel preset env,
• lock down deep diff dependency
• Fix lint error.

[codecov-io]

Codecov Report

:exclamation: No coverage uploaded for pull request base (master@539dab5). Click here to learn what that means. The diff coverage is 0%.

@@           Coverage Diff           @@
##             master   #262   +/-   ##
=======================================
  Coverage          ?    82%           
=======================================
  Files             ?      5           
  Lines             ?    150           
  Branches          ?      0           
=======================================
  Hits              ?    123           
  Misses            ?     27           
  Partials          ?      0

Impacted Files	Coverage Δ
src/core.js	73.33% <0%> (ø)

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