docs(website): convert docs mobile nav from select to nav element and list (#1696)

* website: redo mobile nav to use Link and be rid of select input

* fix react className prop

* add zebapy to contributors

* website: upgrade gatsby deps to release candidate

* fix lint

website/src/components/mobile-nav.js

@@ -1,26 +1,49 @@
 import React, { Component } from 'react';
+import { Link } from 'gatsby';
 
 class MobileNav extends Component {
-  handleChange = event => {
-    this.props.history.push(event.target.value);
+  state = {
+    isOpen: false,
+  };
+  toggleNav = () => {
+    this.setState({
+      isOpen: !this.state.isOpen,
+    });
   };
   render() {
     const { items } = this.props;
+    const { isOpen } = this.state;
 
     return (
-      <div className="mobile docs-nav">
-        <select className="btn-primary" onChange={this.handleChange}>
-          <option>Select A Topic</option>
-          {items.map(item => (
-            <optgroup label={item.title} key={item.title}>
-              {item.group.edges.map(({ node }) => (
-                <option value={node.fields.slug} key={node.fields.slug} className="nav-link">
-                  {node.frontmatter.title}
-                </option>
+      <div className="mobile-docs-nav">
+        <button className="btn-primary mobile-docs-nav-btn" onClick={this.toggleNav}>
+          {isOpen ? <span>&times;</span> : <span>&#9776;</span>} {isOpen ? 'Hide' : 'Show'}{' '}
+          Navigation
+        </button>
+        {isOpen && (
+          <nav className="mobile-docs-nav-content">
+            <ul className="mobile-docs-nav-list">
+              {items.map(item => (
+                <li key={item.title} className="mobile-docs-nav-item">
+                  {item.title}
+                  <ul className="mobile-docs-nav-list">
+                    {item.group.edges.map(({ node }) => (
+                      <li key={node.fields.slug} className="mobile-docs-nav-item">
+                        <Link
+                          to={node.fields.slug}
+                          className="mobile-docs-nav-link"
+                          onClick={this.toggleNav}
+                        >
+                          {node.frontmatter.title}
+                        </Link>
+                      </li>
+                    ))}
+                  </ul>
+                </li>
               ))}
-            </optgroup>
-          ))}
-        </select>
+            </ul>
+          </nav>
+        )}
       </div>
     );
   }