Fix Coveralls submission, and re-enable Coveralls submission from CI

[DilumAluthge]

Fixes #314
Closes #310
Closes #313

[codecov]

Codecov Report

Merging #315 (fe023c7) into master (e0655f8) will increase coverage by 0.51%.
The diff coverage is 100.00%.

❗ Current head fe023c7 differs from pull request most recent head d108113. Consider uploading reports for the commit d108113 to get more accurate results

@@            Coverage Diff             @@
##           master     #315      +/-   ##
==========================================
+ Coverage   90.25%   90.76%   +0.51%     
==========================================
  Files           2        2              
  Lines         195      195              
==========================================
+ Hits          176      177       +1     
+ Misses         19       18       -1     

Impacted Files	Coverage Δ
src/coveralls.jl	94.17% <100.00%> (-1.95%)	⬇️
src/codecovio.jl	86.95% <0.00%> (+3.26%)	⬆️

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update e0655f8...d108113. Read the comment docs.

[vtjnash]

Thanks for tracking that down!

[DilumAluthge]

Your tip to look at lemurheavy/coveralls-public#1527 was spot-on. The issue was indeed that our JSON was not typed the way that Coveralls expected it to be typed.