Disable external Javadoc URLs not supported on JDK 8

This commit comments out (disables) 3 external Javadoc URLs, since the
javadoc tool on JDK 8 cannot access them.

build.gradle

@@ -375,8 +375,9 @@ configure([rootProject] + javaProjects) { project ->
 			"https://tiles.apache.org/tiles-request/apidocs/",
 			"https://tiles.apache.org/framework/apidocs/",
 			"https://www.eclipse.org/aspectj/doc/released/aspectj5rt-api/",
-			"https://www.ehcache.org/apidocs/2.10.4/",
-			"https://www.quartz-scheduler.org/api/2.3.0/",
+			// Temporarily commenting out Ehcache and Quartz since javadoc on JDK 8 cannot access them.
+			// "https://www.ehcache.org/apidocs/2.10.4/",
+			// "https://www.quartz-scheduler.org/api/2.3.0/",
 			"https://www.javadoc.io/doc/com.fasterxml.jackson.core/jackson-core/2.12.7/",
 			"https://www.javadoc.io/doc/com.fasterxml.jackson.core/jackson-databind/2.12.7/",
 			"https://www.javadoc.io/doc/com.fasterxml.jackson.dataformat/jackson-dataformat-xml/2.12.7/",
@@ -388,7 +389,8 @@ configure([rootProject] + javaProjects) { project ->
 			// "https://junit.org/junit5/docs/5.8.2/api/",
 			"https://www.reactive-streams.org/reactive-streams-1.0.3-javadoc/",
 			"https://javadoc.io/static/io.rsocket/rsocket-core/1.1.1/",
-			"https://r2dbc.io/spec/0.8.5.RELEASE/api/",
+			// Temporarily commenting out R2DBC since javadoc on JDK 8 cannot access it.
+			// "https://r2dbc.io/spec/0.8.5.RELEASE/api/",
 			// The external Javadoc link for JSR 305 must come last to ensure that types from
 			// JSR 250 (such as @PostConstruct) are still supported. This is due to the fact
 			// that JSR 250 and JSR 305 both define types in javax.annotation, which results