Allow expires_in equals 0

[runphp]

https://github.com/thephpleague/oauth2-client/pull/606

[codecov-io]

Codecov Report

Merging #791 (b00b6e9) into master (77def43) will not change coverage. The diff coverage is 100.00%.

@@             Coverage Diff             @@
##              master      #791   +/-   ##
===========================================
  Coverage     100.00%   100.00%           
  Complexity       180       180           
===========================================
  Files             20        20           
  Lines            464       466    +2     
===========================================
+ Hits             464       466    +2     

Impacted Files	Coverage Δ
src/Token/AccessToken.php	100.00% <100.00%> (ø)

[ramsey]

Sorry it took so long to review this.

Can you provide more details about why this change is needed? Thanks!