docs: align Maven example to authzed-java 1.5.4 to match the rest of the guide

Author: ivanauth

README.md

@@ -41,7 +41,7 @@ Most commonly, if you are using [Maven] you can add the following to your pom.xm
     <dependency>
         <groupId>com.authzed.api</groupId>
         <artifactId>authzed</artifactId>
-        <version>1.6.0</version>
+        <version>1.5.4</version>
     </dependency>
     <dependency>
         <groupId>io.grpc</groupId>