Set the FSEvents API as the default backend when running on Mac (#54)

Author: sungshik

src/main/java/engineering/swat/watch/impl/jdk/JDKPoller.java

@@ -202,6 +202,8 @@ private static Platform current() {
                         logger.warn("Unexpected value \"{}\" for system property \"{}\". Using value \"jdk\" instead.", val, key);
                         return DEFAULT;
                     }
+                } else {
+                    return MAC;
                 }
             }