Effects: set default easing using jQuery.easing._default

Fixes gh-2219
Close gh-2218

src/effects.js

@@ -289,7 +289,10 @@ function Animation( elem, properties, options ) {
 		animation = deferred.promise({
 			elem: elem,
 			props: jQuery.extend( {}, properties ),
-			opts: jQuery.extend( true, { specialEasing: {} }, options ),
+			opts: jQuery.extend( true, {
+				specialEasing: {},
+				easing: jQuery.easing._default
+			}, options ),
 			originalProperties: properties,
 			originalOptions: options,
 			startTime: fxNow || createFxNow(),