Fix Eclipse compilation error in Gradle plugin

Prior to this commit, the following compilation error presented itself
when importing buildSrc ('spring-build-src') into Eclipse:

    Groovy:missing type for constructor call @ line 36, column 49.

This commit replaces the use of the diamond operator with typical
generics syntax in order to work around the problem. It is assumed that
the underlying problem is to do with the Groovy compiler in use. This
change ensures that any contributor / committer importing
spring-framework into Eclipse has a straightforward experience without
being required to tweak Groovy settings.

If selection of the correct Groovy compilation settings can be made
automatic, then we should of course feel free to use Java 7-style syntax
there in the future.

Note that this was *not* a problem when importing buildSrc into IDEA 12.

buildSrc/src/main/groovy/org/springframework/build/gradle/TestSourceSetDependenciesPlugin.groovy

@@ -33,7 +33,7 @@ class TestSourceSetDependenciesPlugin implements Plugin<Project> {
 	@Override
 	public void apply(Project project) {
 		project.afterEvaluate {
-			Set<ProjectDependency> projectDependencies = new LinkedHashSet<>()
+			Set<ProjectDependency> projectDependencies = new LinkedHashSet<ProjectDependency>()
 			collectProjectDependencies(projectDependencies, project)
 			projectDependencies.each {
 				project.dependencies.add("testCompile", it.dependencyProject.sourceSets.test.output)