Changed the go.cd.elastic-agent.get-icon call to use underscore instead of hyphens.

Author: ketan

src/test/java/cd/go/contrib/elasticagents/docker/executors/GetPluginSettingsIconExecutorTest.java

@@ -34,7 +34,7 @@ public void rendersIconInBase64() throws Exception {
         GoPluginApiResponse response = new GetPluginSettingsIconExecutor().execute();
         HashMap<String, String> hashMap = new Gson().fromJson(response.responseBody(), HashMap.class);
         assertThat(hashMap.size(), is(2));
-        assertThat(hashMap.get("content-type"), is("image/svg+xml"));
+        assertThat(hashMap.get("content_type"), is("image/svg+xml"));
         assertThat(Util.readResourceBytes("/docker-plain.svg"), is(Base64.decodeBase64(hashMap.get("data"))));
     }
 }