Improve styling of groovy and adoc code blocks in the documentation

Closes gh-317

docs/src/docs/asciidoc/getting-started.adoc

@@ -145,7 +145,7 @@ the configuration are described below.
 <6> Using `prepare-package` allows the documentation to be
 	<<getting-started-build-configuration-maven-packaging, included in the package>>.
 
-[source,groovy,indent=0,subs="verbatim,attributes",role="secondary"]
+[source,indent=0,subs="verbatim,attributes",role="secondary"]
 .Gradle
 ----
 	plugins { <1>
@@ -235,7 +235,7 @@ Asciidoctor plugin to ensure that the documentation is generated before it's cop
 <3> Copy the generated documentation into the build output's `static/docs` directory,
 from where it will be included in the jar file.
 
-[source,groovy,indent=0,role="secondary"]
+[source,indent=0,role="secondary"]
 .Gradle
 ----
 	jar {

docs/src/docs/asciidoc/working-with-asciidoctor.adoc

@@ -22,7 +22,7 @@ macro] is used to include generated snippets in your documentation. The `snippet
 attribute specified in the <<getting-started-build-configuration, build configuration>>
 can be used to reference the snippets output directory, for example:
 
-[source,adoc,indent=0]
+[source,indent=0]
 ----
 \include::{snippets}/index/curl-request.adoc[]
 ----
@@ -45,7 +45,7 @@ Asciidoctor has rich support for
 http://asciidoctor.org/docs/user-manual/#cols-format[formatting a table's columns]. For
 example, the widths of a table's columns can be specified using the `cols` attribute:
 
-[source,adoc,indent=0]
+[source,indent=0]
 ----
 [cols=1,3] <1>
 \include::{snippets}/index/links.adoc[]
@@ -60,7 +60,7 @@ three times as wide as the first.
 
 The title of a table can be specified using a line prefixed by a `.`:
 
-[source,adoc,indent=0]
+[source,indent=0]
 ----
 .Links <1>
 \include::{snippets}/index/links.adoc[]