Bump com.squareup.retrofit2:retrofit in /arms-demo/mock-server

Bumps [com.squareup.retrofit2:retrofit](https://github.com/square/retrofit) from 2.3.0 to 2.5.0.
- [Changelog](https://github.com/square/retrofit/blob/master/CHANGELOG.md)
- [Commits](square/retrofit@parent-2.3.0...parent-2.5.0)

---
updated-dependencies:
- dependency-name: com.squareup.retrofit2:retrofit
  dependency-type: direct:production
...

Signed-off-by: dependabot[bot] <support@github.com>

Author: dependabot[bot]

arms-demo/mock-server/pom.xml

@@ -141,7 +141,7 @@
         <dependency>
             <groupId>com.squareup.retrofit2</groupId>
             <artifactId>retrofit</artifactId>
-            <version>2.3.0</version>
+            <version>2.5.0</version>
         </dependency>
         <dependency>
             <groupId>com.squareup.retrofit2</groupId>