Revert "Don't let nginx drop api_key header"

[kevjin]

Reverts #50 which broke CD:

Error: exit status 1
2021/01/31 22:24:50 [emerg] 531#531: "underscores_in_headers" directive is not allowed here in /tmp/nginx-cfg031801590:659
nginx: [emerg] "underscores_in_headers" directive is not allowed here in /tmp/nginx-cfg031801590:659
nginx: configuration file /tmp/nginx-cfg031801590 test failed

Instead of debugging what exactly is wrong, we can just pass "api-key" for now instead (thanks to @uadnan's suggestion)

[codecov]

Codecov Report

Merging #51 (2180782) into main (f7ade54) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##             main      #51   +/-   ##
=======================================
  Coverage   63.52%   63.52%           
=======================================
  Files          21       21           
  Lines         680      680           
=======================================
  Hits          432      432           
  Misses        248      248           

Flag	Coverage Δ
unittests	63.52% <ø> (ø)

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