Run tests against Go 1.15

[flimzy]

No description provided.

[codecov]

Codecov Report

Merging #247 into v3 will decrease coverage by 0.85%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##               v3     #247      +/-   ##
==========================================
- Coverage   89.62%   88.77%   -0.86%     
==========================================
  Files          31       31              
  Lines        2227     1968     -259     
==========================================
- Hits         1996     1747     -249     
+ Misses        167      157      -10     
  Partials       64       64              

Impacted Files	Coverage Δ
chttp/auth.go	50.00% <0.00%> (-10.00%)	⬇️
rows.go	65.25% <0.00%> (-5.04%)	⬇️
bulkget.go	77.77% <0.00%> (-2.23%)	⬇️
chttp/proxyauth.go	66.66% <0.00%> (-1.34%)	⬇️
db.go	80.39% <0.00%> (-1.33%)	⬇️
dbstats.go	92.59% <0.00%> (-0.96%)	⬇️
iter.go	86.23% <0.00%> (-0.95%)	⬇️
chttp/cookieauth.go	93.18% <0.00%> (-0.82%)	⬇️
chttp/chttp.go	93.87% <0.00%> (-0.67%)	⬇️
chttp/trace.go	95.91% <0.00%> (-0.64%)	⬇️
... and 21 more

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