minor: gate passed badge for sonarcloud.io as it is requirements to deploy to Sonarqube repository (checkstyle/checkstyle#5605)

Author: romani

README.md

@@ -66,7 +66,7 @@ In the quality profile, activate some rules from Checkstyle and run an analysis
 [teamcity img]:https://img.shields.io/teamcity/http/teamcity.jetbrains.com/s/Checkstyle_SonarCheckstyleIdeaInspectionsMaster.svg?label=TeamCity%20inspections
 
 [sonar]:https://sonarcloud.io/dashboard?id=com.github.checkstyle%3Acheckstyle-sonar-plugin-parent
-[sonar img]:https://sonarcloud.io/api/project_badges/measure?project=com.github.checkstyle%3Acheckstyle-sonar-plugin-parent&metric=sqale_index
+[sonar img]:https://sonarcloud.io/api/project_badges/measure?project=com.github.checkstyle%3Acheckstyle-sonar-plugin-parent&metric=alert_status
 
 [wercker]: https://app.wercker.com/project/bykey/ece513d8a6eb70207dd3b805b63e8d1c
 [wercker img]: https://app.wercker.com/status/ece513d8a6eb70207dd3b805b63e8d1c/s/master