DATAJPA-1639 - Polishing.

Improved source layout of the changed section.
Fixed one more occurrence of `_Customer` to `Customer_`.

Signed-off-by: Jens Schauder <jschauder@pivotal.io>

src/main/asciidoc/jpa.adoc

@@ -833,7 +833,11 @@ public class CustomerSpecs {
 ----
 ====
 
-Admittedly, the amount of boilerplate leaves room for improvement (that may eventually be reduced by Java 8 closures), but the client side becomes much nicer, as you will see later in this section. The `Customer_` type is a metamodel type generated using the JPA Metamodel generator (see the link:$$https://docs.jboss.org/hibernate/jpamodelgen/1.0/reference/en-US/html_single/#whatisit$$[Hibernate implementation's documentation for an example]). So the expression, `_Customer.createdAt`, assumes the `Customer` has a `createdAt` attribute of type `Date`. Besides that, we have expressed some criteria on a business requirement abstraction level and created executable `Specifications`. So a client might use a `Specification` as follows:
+Admittedly, the amount of boilerplate leaves room for improvement (that may eventually be reduced by Java 8 closures), but the client side becomes much nicer, as you will see later in this section.
+The `Customer_` type is a metamodel type generated using the JPA Metamodel generator (see the link:$$https://docs.jboss.org/hibernate/jpamodelgen/1.0/reference/en-US/html_single/#whatisit$$[Hibernate implementation's documentation for an example]).
+So the expression, `Customer_.createdAt`, assumes the `Customer` has a `createdAt` attribute of type `Date`.
+Besides that, we have expressed some criteria on a business requirement abstraction level and created executable `Specifications`.
+So a client might use a `Specification` as follows:
 
 .Using a simple Specification
 ====