Handle invalid config exit code in gradle plugin

[arturbosch]

Closes #2168

[codecov-io]

Codecov Report

Merging #2193 into master will increase coverage by 0.03%.
The diff coverage is n/a.

@@             Coverage Diff              @@
##             master    #2193      +/-   ##
============================================
+ Coverage     81.12%   81.15%   +0.03%     
- Complexity     2055     2057       +2     
============================================
  Files           339      339              
  Lines          5874     5890      +16     
  Branches       1070     1073       +3     
============================================
+ Hits           4765     4780      +15     
+ Misses          536      535       -1     
- Partials        573      575       +2

Impacted Files	Coverage Δ	Complexity Δ
.../io/gitlab/arturbosch/detekt/cli/runners/Runner.kt	88.88% <ø> (ø)	10 <0> (ø)	⬇️
...in/io/gitlab/arturbosch/detekt/cli/BuildFailure.kt	90.62% <0%> (-4.83%)	1% <0%> (ø)
...n/io/gitlab/arturbosch/detekt/core/DetektFacade.kt	48.78% <0%> (ø)	3% <0%> (ø)	⬇️
...ekt/generator/printer/rulesetpage/ConfigPrinter.kt	75% <0%> (ø)	8% <0%> (ø)	⬇️
...osch/detekt/cli/console/FileBasedFindingsReport.kt	92.59% <0%> (+0.92%)	8% <0%> (+1%)	⬆️
...ab/arturbosch/detekt/cli/console/FindingsReport.kt	94.11% <0%> (+1.26%)	7% <0%> (+1%)	⬆️
...otlin/io/gitlab/arturbosch/detekt/api/CodeSmell.kt	60.46% <0%> (+2.32%)	11% <0%> (ø)	⬇️

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[schalkms]

Looks good.
Can you also please update the docs on the website?
https://arturbosch.github.io/detekt/cli.html

[arturbosch]

Good catch, updated. Thanks!