chore: fix the typos in comments (#2679)

website/content/docs/nextjs.md

@@ -20,7 +20,7 @@ npm init -y
 # Install required dependencies
 npm install --save react react-dom next
 
-# Intall webpack loader for Markdown
+# Install webpack loader for Markdown
 npm install --save-dev frontmatter-markdown-loader
 
 # Create folder for pages (default for NextJS), and add a index file

website/src/components/docs-nav.js

@@ -2,7 +2,7 @@ import React, { Component } from 'react';
 import Link from 'gatsby-link';
 
 /**
- * Maually get table of contents since tableOfContents from markdown
+ * Manually get table of contents since tableOfContents from markdown
  * nodes have code added.
  *
  * https://github.com/gatsbyjs/gatsby/issues/5436