lib: show stderr when getting project from npm fails

[addaleax]

Checklist

• npm test passes (mostly – but failures seem unrelated)
• tests are included
• contribution guidelines followed
  here

[codecov-io]

Codecov Report

Merging #753 into master will decrease coverage by 0.77%.
The diff coverage is 88.88%.

@@            Coverage Diff             @@
##           master     #753      +/-   ##
==========================================
- Coverage   96.22%   95.44%   -0.78%     
==========================================
  Files          27       27              
  Lines         874      879       +5     
==========================================
- Hits          841      839       -2     
- Misses         33       40       +7

Impacted Files	Coverage Δ
lib/grab-project.js	92.15% <88.88%> (+0.85%)	⬆️
lib/spawn.js	66.66% <0%> (-33.34%)	⬇️
lib/match-conditions.js	91.48% <0%> (-2.13%)	⬇️
bin/citgm.js	98.07% <0%> (-1.93%)	⬇️
bin/citgm-all.js	91.17% <0%> (-0.99%)	⬇️

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