Use new update site for Spring Java Format's Eclipse plugin

See gh-26167

CONTRIBUTING.adoc

@@ -111,7 +111,7 @@ Spring Boot includes project specific source formatting settings, in order to ha
 
 ===== Install the Spring Formatter plugin
 * Select "`Help`" -> "`Install New Software`".
-* Add `https://dl.bintray.com/spring/javaformat-eclipse/` as a site.
+* Add `https://repo.spring.io/javaformat-eclipse-update-site/` as a site.
 * Install "Spring Java Format".
 
 NOTE: The plugin is optional.

eclipse/spring-boot-project.setup

@@ -91,7 +91,7 @@
     <requirement
         name="org.eclipse.buildship.oomph.feature.group"/>
     <repository
-        url="https://dl.bintray.com/spring/javaformat-eclipse/"/>
+        url="https://repo.spring.io/javaformat-eclipse-update-site/"/>
     <repository
         url="https://repo1.maven.org/maven2/.m2e/connectors/m2eclipse-buildhelper/0.15.0/N/0.15.0.201405280027/"/>
     <repository