GH-1000 - Update version number in README.

Author: odrotbohm

readme.adoc

@@ -18,7 +18,7 @@ It supports the link:{docs}#verification[verification] of such modular arrangeme
     <dependency>
       <groupId>org.springframework.modulith</groupId>
       <artifactId>spring-modulith-bom</artifactId>
-      <version>1.2.4</version>
+      <version>1.3.1</version>
       <scope>import</scope>
       <type>pom</type>
     </dependency>