Change minimum Node version to 10

[malept]

• I have read the contribution documentation for this project.
• I agree to follow the code of conduct that this project follows, as appropriate.
• The changes are appropriately documented (if applicable).
• The changes have sufficient test coverage (if applicable).
• The testsuite passes successfully on my local machine (if applicable).

Summarize your changes:

Certain dependencies now require Node 10 (notably, semver).

[codecov]

Codecov Report

Merging #62 into master will not change coverage.
The diff coverage is n/a.

@@          Coverage Diff          @@
##           master    #62   +/-   ##
=====================================
  Coverage     100%   100%           
=====================================
  Files           8      8           
  Lines         252    252           
=====================================
  Hits          252    252

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