clarified build.gradle: "compile" stopped working in gradle 6.x / 7.x for unknown reasons;

--- a/src/Pure/Tools/scala_project.scala	Mon Aug 02 13:30:56 2021 +0200
+++ b/src/Pure/Tools/scala_project.scala	Mon Aug 02 13:50:45 2021 +0200
@@ -161,7 +161,7 @@
 
 dependencies {
   implementation 'org.scala-lang:scala-library:""" + scala.util.Properties.versionNumberString + """'
-  compile files(
+  compileOnly files(
     """ + jars.map(jar => groovy_string(File.platform_path(jar))).mkString("", ",\n    ", ")") +
 """
 }