don’t mutate props.style

Author: ryanflorence

modules/Link.js

@@ -81,11 +81,11 @@ export var Link = React.createClass({
 
     // ignore if rendered outside of the context of a router, simplifies unit testing
     if (router && router.isActive(to, query)) {
-      if (props.activeClassName) 
+      if (props.activeClassName)
         props.className += props.className !== '' ? ` ${props.activeClassName}` : props.activeClassName;
 
       if (props.activeStyle)
-        Object.assign(props.style, props.activeStyle);
+        props.style = Object.assign({}, props.style, props.activeStyle);
     }
 
     return React.createElement('a', props);