BATCH-2673: fix the PDF version of the reference documentation

Before this commit, the file name and content of the PDF version of
the reference documentation were incorrect. The file was empty and
named "toggle.pdf" instead of "spring-batch-reference.pdf".

This commit fixes the PDF file name and content.

Resolves BATCH-2673

build.gradle

@@ -743,7 +743,7 @@ task docsZip(type: Zip) {
 			exclude 'pdf/common-patterns.pdf'
 			exclude 'pdf/domain.pdf'
 			exclude 'pdf/index.pdf'
-			exclude 'pdf/index-single.pdf'
+			exclude 'pdf/toggle.pdf'
 			exclude 'pdf/job.pdf'
 			exclude 'pdf/jsr-352.pdf'
 			exclude 'pdf/readersAndWriters.pdf'
@@ -759,6 +759,8 @@ task docsZip(type: Zip) {
 			exclude 'pdf/whatsnew.pdf'
 			exclude 'pdf/glossary.pdf'
 
+			rename  'index-single.pdf', 'spring-batch-reference.pdf'
+
 			into 'reference'
 		}
 }