Remove key parameter from replace and use React.cloneElement

The previous implementation was to pass the `key` as the 2nd
parameter in `replace` method and force the user to set the
"key" prop in their custom React element.

This creates further complexity for the end-user.

As a result, use `React.cloneElement` which does the same thing
without additional work from the user.

`React.cloneElement` takes the React element and merges the
"key" prop taken from the array index with the original
element's props when applicable.

https://facebook.github.io/react/docs/top-level-api.html#react.cloneelement

Author: remarkablemark

lib/dom-to-react.js

@@ -28,9 +28,14 @@ function domToReact(nodes, options) {
 
         // replace with custom React element (if applicable)
         if (isReplacePresent) {
-            replacement = options.replace(node, i); // i = key
+            replacement = options.replace(node);
 
             if (React.isValidElement(replacement)) {
+                // specify a "key" prop if element has siblings
+                // https://fb.me/react-warning-keys
+                if (len > 1) {
+                    replacement = React.cloneElement(replacement, { key: i });
+                }
                 result.push(replacement);
                 continue;
             }

test/html-to-react.js

@@ -77,9 +77,9 @@ describe('html-to-react', function() {
             it('overrides the element if replace is valid', function() {
                 var html = data.html.complex;
                 var reactElement = Parser(html, {
-                    replace: function(node, key) {
+                    replace: function(node) {
                         if (node.name === 'title') {
-                            return React.createElement('title', { key: key }, 'Replaced Title');
+                            return React.createElement('title', {}, 'Replaced Title');
                         }
                     }
                 });