Polish "Add Grails sample app" (1338df9)

The sole structural change is to rearrange the build slightly so that,
like the other samples, the version of the Grails sample's REST Docs
dependency is automatically updated.

See gh-250

buildSrc/src/main/groovy/org/springframework/restdocs/build/SampleBuildConfigurer.groovy

@@ -61,6 +61,9 @@ public class SampleBuildConfigurer {
 				replaceVersion(new File(this.workingDir, 'build.gradle'),
 						"ext\\['spring-restdocs.version'\\] = '.*'",
 						"ext['spring-restdocs.version'] = '${project.version}'")
+				replaceVersion(new File(this.workingDir, 'build.gradle'),
+						"restDocsVersion = \".*\"",
+						"restDocsVersion = \"${project.version}\"")
 			}
 		}
 		else if (new File(sampleDir, 'pom.xml').isFile()) {