fix rendering of provider schema reference in response body

[fmigneault]

Fixes

• Fix GET /providers/{provider_id} response using $schema instead of $id to provide its content schema.

relates to #551

[codecov]

Codecov Report

Merging #555 (c6a351f) into master (a0b3d21) will increase coverage by 0.00%.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##           master     #555   +/-   ##
=======================================
  Coverage   84.42%   84.43%           
=======================================
  Files          79       79           
  Lines       17633    17637    +4     
  Branches     2674     2674           
=======================================
+ Hits        14886    14891    +5     
  Misses       2019     2019           
+ Partials      728      727    -1     

Files Changed	Coverage Δ
weaver/wps_restapi/providers/providers.py	85.50% <100.00%> (+0.32%)	⬆️
weaver/wps_restapi/swagger_definitions.py	99.82% <100.00%> (+<0.01%)	⬆️
weaver/wps_restapi/utils.py	80.89% <100.00%> (+1.12%)	⬆️