use symfony/yaml 4.0 if available

[aaronpk]

No description provided.

[codecov-io]

Codecov Report

Merging #12 into develop will increase coverage by 4.57%.
The diff coverage is n/a.

@@              Coverage Diff              @@
##             develop      #12      +/-   ##
=============================================
+ Coverage      22.82%   27.39%   +4.57%     
  Complexity        91       91              
=============================================
  Files             10       10              
  Lines            276      219      -57     
=============================================
- Hits              63       60       -3     
+ Misses           213      159      -54

Impacted Files	Coverage Δ	Complexity Δ
src/JwtVerifierBuilder.php	70.96% <0%> (-0.91%)	9% <0%> (ø)
src/Adaptors/FirebasePhpJwt.php	0% <0%> (ø)	31% <0%> (ø)	⬇️
src/Request.php	100% <0%> (ø)	9% <0%> (ø)	⬇️
src/Discovery/Oidc.php	0% <0%> (ø)	1% <0%> (ø)	⬇️
src/Jwt.php	0% <0%> (ø)	11% <0%> (ø)	⬇️
src/Adaptors/AutoDiscover.php	0% <0%> (ø)	3% <0%> (ø)	⬇️
src/JwtVerifier.php	36.84% <0%> (+1.95%)	21% <0%> (ø)	⬇️

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