Remove static Boot version from documentation

Closes gh-10774

spring-boot-docs/src/main/asciidoc/using-spring-boot.adoc

@@ -301,14 +301,14 @@ To declare dependencies a typical `ivy.xml` file will look something like this:
 
 A typical `build.xml` will look like this:
 
-[source,xml,indent=0]
+[source,xml,indent=0,subs="verbatim,quotes,attributes"]
 ----
 	<project
 		xmlns:ivy="antlib:org.apache.ivy.ant"
 		xmlns:spring-boot="antlib:org.springframework.boot.ant"
 		name="myapp" default="build">
 
-		<property name="spring-boot.version" value="1.3.0.BUILD-SNAPSHOT" />
+		<property name="spring-boot.version" value="{spring-boot-version}" />
 
 		<target name="resolve" description="--> retrieve dependencies with ivy">
 			<ivy:retrieve pattern="lib/[conf]/[artifact]-[type]-[revision].[ext]" />