Added @cboden's suggestion of adding "and PHP5 only" to the LibEventLoop suggest

Author: WyriHaximus

composer.json

@@ -10,7 +10,7 @@
         "phpunit/phpunit": "~4.8"
     },
     "suggest": {
-        "ext-libevent": ">=0.1.0 for LibEventLoop",
+        "ext-libevent": ">=0.1.0 for LibEventLoop and PHP5 only",
         "ext-event": "~1.0 for ExtEventLoop",
         "ext-libev": "for LibEvLoop"
     },