fix: undefined headers breaks compatibility with auth

[bcoe]

allowing an undefined value for header values breaks compatibility withgoogle-auth-library-nodejs:

                                 ~~~~~~~~~~~~~~~~~

test/test.jwt.ts:273:19 - error TS2532: Object is possibly 'undefined'.

273   const decoded = got.Authorization.replace('Bearer ', '');
                      ~~~~~~~~~~~~~~~~~

test/test.jwtaccess.ts:61:30 - error TS2532: Object is possibly 'undefined'.

61   const decoded = jws.decode(headers.Authorization.replace('Bearer ', ''));
                                ~~~~~~~~~~~~~~~~~~~~~

test/test.jwtaccess.ts:72:30 - error TS2532: Object is possibly 'undefined'.

72   const decoded = jws.decode(headers.Authorization.replace('Bearer ', ''));

Unless we have a pressing need to set undefined headers, I recommend we revert this change for the time being.

[codecov]

Codecov Report

Merging #66 into master will increase coverage by 0.09%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master      #66      +/-   ##
==========================================
+ Coverage   67.82%   67.91%   +0.09%     
==========================================
  Files           1        1              
  Lines         345      346       +1     
  Branches       28       28              
==========================================
+ Hits          234      235       +1     
  Misses        110      110              
  Partials        1        1

Impacted Files	Coverage Δ
src/index.ts	67.91% <100%> (+0.09%)	⬆️

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[callmehiphop]

Is this technically a breaking change?

[JustinBeckwith]

Nope! It's loosening the accepted values, not making them stricter, so I'm ok with it :)

[callmehiphop]

Oh whoops, I didn't realize it was any. Ignore me, lol.