Flag spring-cloud-starter-task temporarily as a non starter

This commit sets the `starter` flag of `spring-cloud-starter-task` to
`true` to force the core starter to be added when only that dependency
is selected.

See https://github.com/spring-cloud/spring-cloud-task/issues/359

Closes gh-566

initializr-service/src/main/resources/application.yml

@@ -729,6 +729,7 @@ initializr:
           artifactId: spring-cloud-starter-task
           versionRange: "1.3.0.RELEASE"
           bom: spring-cloud-task
+          starter: false
           mappings:
             - versionRange: "[1.3.0.RELEASE,1.3.x.RELEASE]"
               artifactId: spring-cloud-task-starter