Ensure spring-core JAR is reproducible

Prior to this commit, a change to Javadoc in any class in spring-core
would result in ALL tests in the entire test suite being re-run via the
Gradle build.

Thanks to a tip from @melix, this commit aims to ensure that the
spring-core JAR is "reproducible".

spring-core/spring-core.gradle

@@ -72,6 +72,9 @@ dependencies {
 }
 
 jar {
+	reproducibleFileOrder = true
+	preserveFileTimestamps = false // maybe not necessary here, but good for reproducibility
+
 	// Inline repackaged cglib classes directly into spring-core jar
 	dependsOn cglibRepackJar
 	from(zipTree(cglibRepackJar.archivePath)) {