pass context.Consumer to mapContextToProps

As outlined in react-restart/context#9, context toolbox
needs to only use Context.Consumer since it can't
navigate to the Consumer property reliably.

src/AbstractNav.js

@@ -132,7 +132,7 @@ class AbstractNav extends React.Component {
 }
 
 export default mapContextToProps(
-  [SelectableContext, TabContext],
+  [SelectableContext.Consumer, TabContext.Consumer],
   (parentOnSelect, tabContext, { role }) => {
     if (!tabContext) return { parentOnSelect };
 

src/DropdownItem.js

@@ -98,7 +98,7 @@ class DropdownItem extends React.Component {
 }
 
 export default mapContextToProps(
-  [SelectableContext, NavContext],
+  [SelectableContext.Consumer, NavContext.Consumer],
   (onSelect, navContext, props) => {
     const { activeKey } = navContext || {};
     const key = makeEventKey(props.eventKey, props.href);

www/src/components/Heading.js

@@ -43,7 +43,7 @@ class Heading extends React.Component {
 }
 
 export default mapContextToProps(
-  TocContext,
+  TocContext.Consumer,
   c => ({ registerNode: c.registerNode }),
   Heading,
 );