Lint JS w/out extension too

[raphinesse]

This uses npm-run-all to run the two ESLint invocations unconditionally in sequence while still preserving the error code.

[codecov-io]

Codecov Report

Merging #453 into master will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master     #453   +/-   ##
=======================================
  Coverage   44.27%   44.27%           
=======================================
  Files          17       17           
  Lines        1694     1694           
  Branches      311      311           
=======================================
  Hits          750      750           
  Misses        944      944

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