Update swaggest/json-schema to fix const handling

[vearutop]

Fixes #40.

[codecov]

Codecov Report

Merging #41 (ec77401) into master (ec0b9e8) will increase coverage by 0.05%.
The diff coverage is n/a.

@@             Coverage Diff              @@
##             master      #41      +/-   ##
============================================
+ Coverage     86.74%   86.80%   +0.05%     
  Complexity      667      667              
============================================
  Files            40       40              
  Lines          1735     1735              
============================================
+ Hits           1505     1506       +1     
+ Misses          230      229       -1     

Impacted Files	Coverage Δ
src/JsonSchema/PhpBuilder.php	85.00% <0.00%> (+0.55%)	⬆️

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