Fix maven documentation : groupId
Fix maven documentation : groupId

groupId is wrong.
Should be `io.gatling.highcharts` as the sample
https://github.com/gatling/gatling-maven-plugin-demo/blob/master/pom.xml
ryez/gatling,gatling/gatling,MykolaB/gatling,timve/gatling,timve/gatling,thkluge/gatling,MykolaB/gatling,gatling/gatling,thkluge/gatling,gatling/gatling,GabrielPlassard/gatling,GabrielPlassard/gatling,wiacekm/gatling,GabrielPlassard/gatling,wiacekm/gatling,ryez/gatling,gatling/gatling,gatling/gatling,thkluge/gatling,MykolaB/gatling,pwielgolaski/gatling,MykolaB/gatling,pwielgolaski/gatling,wiacekm/gatling,timve/gatling,wiacekm/gatling,timve/gatling,wiacekm/gatling,GabrielPlassard/gatling,thkluge/gatling,ryez/gatling,ryez/gatling,pwielgolaski/gatling,pwielgolaski/gatling