Merge pull request #3317 from wing328/retrofit1_wording

[Java][Retrofit] update wording for java retrofit1

Author: wing328

modules/swagger-codegen/src/main/java/io/swagger/codegen/languages/JavaClientCodegen.java

@@ -36,7 +36,7 @@ public JavaClientCodegen() {
         supportedLibraries.put("feign", "HTTP client: Netflix Feign 8.16.0. JSON processing: Jackson 2.7.0");
         supportedLibraries.put("jersey2", "HTTP client: Jersey client 2.22.2. JSON processing: Jackson 2.7.0");
         supportedLibraries.put("okhttp-gson", "HTTP client: OkHttp 2.7.5. JSON processing: Gson 2.6.2");
-        supportedLibraries.put(RETROFIT_1, "HTTP client: OkHttp 2.7.5. JSON processing: Gson 2.3.1 (Retrofit 1.9.0)");
+        supportedLibraries.put(RETROFIT_1, "HTTP client: OkHttp 2.7.5. JSON processing: Gson 2.3.1 (Retrofit 1.9.0). IMPORTANT NOTE: retrofit1.x is no longer actively maintained so please upgrade to 'retrofit2' instead.");
         supportedLibraries.put(RETROFIT_2, "HTTP client: OkHttp 3.2.0. JSON processing: Gson 2.6.1 (Retrofit 2.0.2). Enable the RxJava adapter using '-DuseRxJava=true'. (RxJava 1.1.3)");
 
         CliOption libraryOption = new CliOption(CodegenConstants.LIBRARY, "library template (sub-template) to use");