Use correct version when linking to Spring and Spring Security docs

Closes gh-1621

Author: wilkinsona

spring-boot-docs/pom.xml

@@ -217,6 +217,8 @@
 										<spring-boot-version>${project.version}</spring-boot-version>
 										<spring-boot-docs-version>${project.version}</spring-boot-docs-version>
 										<spring-boot-repo>${spring-boot-repo}</spring-boot-repo>
+										<spring-docs-version>${spring.version}</spring-docs-version>
+										<spring-security-docs-version>${spring-security.version}</spring-security-docs-version>
 										<github-tag>${github-tag}</github-tag>
 									</attributes>
 								</configuration>

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

@@ -27,9 +27,9 @@ Phillip Webb; Dave Syer; Josh Long; Stéphane Nicoll; Rob Winch; Andy Wilkinson;
 :dc-spring-boot-autoconfigure: {dc-root}/org/springframework/boot/autoconfigure
 :dc-spring-boot-actuator: {dc-root}/org/springframework/boot/actuate
 :spring-boot-maven-plugin-site: http://docs.spring.io/spring-boot/docs/{spring-boot-docs-version}/maven-plugin
-:spring-reference: http://docs.spring.io/spring/docs/current/spring-framework-reference/htmlsingle
-:spring-security-reference: http://docs.spring.io/spring-security/site/docs/current/reference/htmlsingle
-:spring-javadoc: http://docs.spring.io/spring/docs/current/javadoc-api/org/springframework
+:spring-reference: http://docs.spring.io/spring/docs/{spring-docs-version}/spring-framework-reference/htmlsingle
+:spring-security-reference: http://docs.spring.io/spring-security/site/docs/{spring-security-docs-version}/reference/htmlsingle
+:spring-javadoc: http://docs.spring.io/spring/docs/{spring-docs-version}/javadoc-api/org/springframework
 :spring-data-javadoc: http://docs.spring.io/spring-data/jpa/docs/current/api/org/springframework/data/jpa
 :spring-data-commons-javadoc: http://docs.spring.io/spring-data/commons/docs/current/api/org/springframework/data
 :spring-data-mongo-javadoc: http://docs.spring.io/spring-data/mongodb/docs/current/api/org/springframework/data/mongodb