feat(cli): bumped unofficial generator version to 8.1

Author: DmitrySboychakov

openapi-generator-cli/lib/openapi-generator.jar

@@ -53,7 +53,7 @@
         <dependency>
             <groupId>com.bluetrainsoftware.maven</groupId>
             <artifactId>openapi-dart-generator</artifactId>
-            <version>7.2</version>
+            <version>8.1</version>
         </dependency>
     </dependencies>
 </project>