Eleminate now-redundant if block. Add change-log notes.

docs/change-log.md

@@ -27,6 +27,7 @@
 
 - API: `m.route.set()` causes all mount points to be redrawn ([#1592](https://github.com/MithrilJS/mithril.js/pull/1592))
 - API: If a user sets the Content-Type header within a request's options, that value will be the entire header value rather than being appended to the default value ([#1924](https://github.com/MithrilJS/mithril.js/pull/1924))
+- API: Using style objects in hyperscript calls will now properly diff style properties from one render to another as opposed to re-writing all element style properties every render.
 
 ---
 

render/render.js

@@ -572,11 +572,6 @@ module.exports = function($window) {
 			for (var key in style) {
 				element.style[key] = style[key]
 			}
-			if (old != null && typeof old !== "string") {
-				for (var key in old) {
-					if (!(key in style)) element.style[key] = ""
-				}
-			}
 		}
 	}