fix: fix themes roadmap blog post date (#12532)

* fix: fix themes roadmap blog post date

* remove duplicated title and adjust section title to h2

Author: pieh

docs/blog/2018-03-11-gatsby-themes-roadmap/index.md docs/blog/2019-03-11-gatsby-themes-roadmap/index.md

@@ -1,13 +1,11 @@
 ---
 title: Gatsby Themes Roadmap
-date: 2018-03-11
+date: 2019-03-11
 author: Chris Biscardi
 excerpt: "Where Gatsby themes are headed in 2019"
 tags: ["themes", "architecture"]
 ---
 
-# Gatsby Themes Roadmap
-
 Gatsby themes have come a long way in the last few months. We've iteratively
 shipped functionality that has enabled people to ship sites quickly on short
 deadline with an absolute minimum (1) of breaking changes. In this post we'll
@@ -19,7 +17,7 @@ like for where we're going:
 3. Simplifying the Data Model
 4. ?
 
-# Theme Composition
+## Theme Composition
 
 The core theme composition algorithm was the first set of functionality we
 worked on. This piece of the code at its core can be thought of as
@@ -77,7 +75,7 @@ what best practices will end up being and if you're just getting started its a
 good idea to build out a single theme before attempting to build a set of themes
 that work together.
 
-# Component Shadowing
+## Component Shadowing
 
 The next problem we approached can be described as "How do I change the
 navigation component in a theme?".
@@ -106,7 +104,7 @@ To learn more about child themes and component shadowing, [read this themes
 update blog
 post](https://www.gatsbyjs.org/blog/2019-01-29-themes-update-child-theming-and-component-shadowing/).
 
-# Improving Documentation
+## Improving Documentation
 
 After composition and shadowing were released, we focused a bit on fixing any
 bugs that popped up and expanding usage to a wider audience. Some companies have
@@ -121,7 +119,7 @@ on other platforms.
 We've also written and are updating a set of documentation that will be released
 on gatsbyjs.org for anyone that is using or looking to start using themes.
 
-# Simplifying the Data Model
+## Simplifying the Data Model
 
 We shipped composition, child themes, and component shadowing and we're not
 stopping there. Next up on our plate is something you may have seen us tweeting
@@ -151,7 +149,7 @@ We're still experimenting and doing research here so I won't show any code
 today. If you want to participate in the development of the data abstraction, I
 highly encourage you to install `gatsby@schema-customization` and play around.
 
-# The Future
+## The Future
 
 There are a number of directions we can go from here to give a better user
 experience to developing and using themes for experienced Gatsby contributors