Hide TOC menu when onPageNav is not separate (#768)

* (bug) - Mobile menu when onPageNav is separate

* fixed lint

* fixed lint

* removed whitespace in brackets

* refactored

* refactor

* Prettier

lib/core/nav/SideNav.js

@@ -28,9 +28,11 @@ class SideNav extends React.Component {
                   {this.getLocalizedCategoryString(this.props.current.category)}
                 </span>
               </h2>
+              {siteConfig.onPageNav === 'separate' && (
                 <div className="tocToggler" id="tocToggler">
                   <i className="icon-toc" />
                 </div>
+              )}
             </div>
             <div className="navGroups">
               {this.props.contents.map(this.renderCategory, this)}