Start building against Spring REST Docs 1.2.1 snapshots

See gh-9071

spring-boot-dependencies/pom.xml

@@ -165,7 +165,7 @@
 		<spring-loaded.version>1.2.7.RELEASE</spring-loaded.version>
 		<spring-mobile.version>2.0.0.M1</spring-mobile.version>
 		<spring-plugin.version>1.2.0.RELEASE</spring-plugin.version>
-		<spring-restdocs.version>1.2.0.RELEASE</spring-restdocs.version>
+		<spring-restdocs.version>1.2.1.BUILD-SNAPSHOT</spring-restdocs.version>
 		<spring-retry.version>1.2.0.RELEASE</spring-retry.version>
 		<spring-security.version>5.0.0.BUILD-SNAPSHOT</spring-security.version>
 		<spring-security-jwt.version>1.0.7.RELEASE</spring-security-jwt.version>