Hide bsStyle from Modal props documentation

Fixes react-bootstrap#1147

Author: taion

src/Modal.js

@@ -127,7 +127,13 @@ const Modal = React.createClass({
      * Consider leaving the default value here, as it is necessary to make the Modal work well with assistive technologies,
      * such as screen readers.
      */
-    enforceFocus: React.PropTypes.bool
+    enforceFocus: React.PropTypes.bool,
+
+    /**
+     * Hide this from automatic props documentation generation.
+     * @private
+     */
+    bsStyle: React.PropTypes.string
   },
 
   getDefaultProps() {