Stop clearing buffer reference

The buffer reference was being lost when clearing the array. This reference is helpful when rendering on the server with other libraries besides Metal (such as React).

packages/incremental-dom-string/src/core.js

@@ -38,7 +38,7 @@ const patch = function(node, fn, data) {
 	currentParent = node;
 	fn(data);
 	currentParent.innerHTML = buffer.join('');
-	buffer = [];
+	buffer.splice(0, buffer.length);
 	return currentParent;
 };