Minor documentation polish

Author: philwebb

spring-boot-docs/src/main/asciidoc/production-ready-features.adoc

@@ -355,7 +355,7 @@ You can then refer to your Gradle project's properties via placeholders, e.g.
 ----
 
 NOTE: Gradle's `expand` method uses Groovy's `SimpleTemplateEngine` which transforms
-`${..}` tokens. This `${..}` style conflicts with Spring's own property placeholder
+`${..}` tokens. The `${..}` style conflicts with Spring's own property placeholder
 mechanism. To use Spring property placeholders together with automatic expansion
 the Spring property placeholders need to be escaped like `\${..}`.