Add fix and test case for orderBy argument as a variable

[anotender]

Fixes #194

[codecov]

Codecov Report

Merging #195 into master will decrease coverage by 0.03%.
The diff coverage is 100%.

@@             Coverage Diff              @@
##             master     #195      +/-   ##
============================================
- Coverage     73.68%   73.64%   -0.04%     
- Complexity      874      876       +2     
============================================
  Files            50       50              
  Lines          3701     3703       +2     
  Branches        627      623       -4     
============================================
  Hits           2727     2727              
- Misses          696      697       +1     
- Partials        278      279       +1

Impacted Files	Coverage Δ	Complexity Δ
...a/query/schema/impl/QraphQLJpaBaseDataFetcher.java	75.82% <100%> (+0.2%)	170 <6> (+3)	⬆️
...jpa/query/schema/impl/GraphQLJpaSchemaBuilder.java	91.2% <100%> (ø)	118 <0> (ø)	⬇️
.../graphql/jpa/query/introspection/Constructors.java	78% <0%> (-4%)	14% <0%> (-1%)
...tures/graphql/jpa/query/introspection/Methods.java	80.43% <0%> (-0.42%)	13% <0%> (ø)
...es/graphql/jpa/query/introspection/Properties.java	88.15% <0%> (-0.16%)	24% <0%> (ø)
...ntures/graphql/jpa/query/introspection/Fields.java	96.66% <0%> (-0.11%)	11% <0%> (ø)

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[igdianov]

Great PR @anotender! Thank you for contribution!