upgrade connection error log from warn to error

We had a connectivity issue between the client and ld-relay due to some
misconfiguration. It resulted in apps not being able to connect to
LaunchDarkly for a long time.

It took a while to realize that the SDK actually logged a warning. It'd
be nice if this was an error.

Author: mightyguava

src/main/java/com/launchdarkly/client/StreamProcessor.java

@@ -185,7 +185,7 @@ public void onComment(String comment) {
 
       @Override
       public void onError(Throwable throwable) {
-        logger.warn("Encountered EventSource error: {}", throwable.toString());
+        logger.error("Encountered EventSource error: {}", throwable.toString());
         logger.debug(throwable.toString(), throwable);
       }
     };