Update index.d.ts

bsStyle can be used on DropdownToggle too.

react-bootstrap/index.d.ts

@@ -206,6 +206,7 @@ declare namespace ReactBootstrap {
         title?: string;
         useAnchor?: boolean;
         bsClass?:string; // Added since v0.30.0
+        bsStyle?:string;
     }
     class DropdownToggle extends React.Component<DropdownToggleProps, any> { }