Fix coverage and testing badges

[cspotcode]

Codecov reports 75% coverage; coveralls reports 82%. I might try to figure out the discrepancy, but that's pretty low-priority.

EDIT: codecov explains their formula here:
https://docs.codecov.io/docs/about-code-coverage#codecov-calculations

I couldn't find a clear doc for coveralls, though I see it reporting both branch coverage percentage, and "relevant lines covered" percentage. codecov's number is somewhere between these two.

[codecov]

Codecov Report

Merging #1095 into master will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master    #1095   +/-   ##
=======================================
  Coverage   75.49%   75.49%           
=======================================
  Files           7        7           
  Lines         657      657           
  Branches      148      148           
=======================================
  Hits          496      496           
  Misses        107      107           
  Partials       54       54           

Flag	Coverage Δ
#node_10	72.15% <ø> (ø)
#node_12_15	72.53% <ø> (ø)
#node_12_16	72.53% <ø> (ø)
#node_13	75.19% <ø> (ø)
#node_14	75.19% <ø> (ø)
#typescript_2_7	75.03% <ø> (ø)
#typescript_latest	74.27% <ø> (ø)
#typescript_next	74.12% <ø> (ø)
#ubuntu	75.19% <ø> (ø)
#windows	75.34% <ø> (ø)

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[coveralls]

Coverage increased (+1.0%) to 83.175% when pulling 141c4e1 on ab/fix-coverage-and-test-badges into 490ed8a on master.