ObjectChecker#getGitsubmodules: Fix malformed javadoc

The text "<tree, blob>" with angle brackets should not be used in javadoc
since it is interpreted as an HTML tag and then rejected since it's not a
valid HTML tag. Wrap the text in a @literal tag.

Also add a missing space.

Change-Id: Ide045e8c04a39a916f5b2e964e58c151e4555830
Signed-off-by: David Pursehouse <david.pursehouse@gmail.com>

org.eclipse.jgit/src/org/eclipse/jgit/lib/ObjectChecker.java

@@ -1213,7 +1213,7 @@ public class ObjectChecker {
 	 * its blob id (e.g. to validate its contents) and the tree where it was
 	 * found (e.g. to check if it is in the root)
 	 *
-	 * @return List of pairs of ids <tree, blob>
+	 * @return List of pairs of ids {@literal <tree, blob>}.
 	 *
 	 * @since 4.7.5
 	 */