Merge pull request react-bootstrap#1295 from tannewt/patch-1

Set the disabled css class so that the text is greyed out.

Author: taion

src/Dropdown.js

@@ -89,6 +89,7 @@ class Dropdown extends React.Component {
 
     const rootClasses = {
       open: this.props.open,
+      disabled: this.props.disabled,
       dropdown: !this.props.dropup,
       dropup: this.props.dropup
     };