Grammar fixes in tutorial. (#4928)

Signed-off-by: Tim Whiteaker <[email protected]>

docs/tutorial/part-six/index.md

@@ -5,7 +5,7 @@ typora-copy-images-to: ./
 
 ## What's in this tutorial?
 
-The previous tutorial showed how source plugins bring data _into_ Gatsby’s data system. In this tutorial,you'll learn how transformer plugins _transform_ the raw content brought by source plugins. The combination of source plugins and transformer plugins can handle all data sourcing and data transformation you might need when building a Gatsby site.
+The previous tutorial showed how source plugins bring data _into_ Gatsby’s data system. In this tutorial, you'll learn how transformer plugins _transform_ the raw content brought by source plugins. The combination of source plugins and transformer plugins can handle all data sourcing and data transformation you might need when building a Gatsby site.
 
 ## Transformer plugins
 
@@ -191,7 +191,7 @@ Try creating a new page containing a blog post and see what happens to the list
 ## What's coming next?
 
 This is great! We've just created a nice index page where we're querying our Markdown
-files and produces a list of blogpost titles and excerpts. But we don't want to just see excerpts, we want actual pages for our Markdown files.
+files and producing a list of blogpost titles and excerpts. But we don't want to just see excerpts, we want actual pages for our Markdown files.
 
 We could continue to create pages by placing React components in `src/pages`. However, we'll
 next learn how to _programmatically_ create pages from _data_. Gatsby is _not_

docs/tutorial/part-three/index.md

@@ -19,7 +19,7 @@ Let's dive in and explore Gatsby layouts.
 
 ## Install a starter
 
-As we mentioned in Part Two, at this point it's probably a good idea to close the terminal window(s) and project files from previous parts of the tutorial, to keep things clean on your desktop. Then, open a new terminal window and and run the following commands to create a new Gatsby site in a directory called `tutorial-part-three` and then move to this new directory:
+As we mentioned in Part Two, at this point it's probably a good idea to close the terminal window(s) and project files from previous parts of the tutorial, to keep things clean on your desktop. Then, open a new terminal window and run the following commands to create a new Gatsby site in a directory called `tutorial-part-three` and then move to this new directory:
 
 ```shell
 gatsby new tutorial-part-three https://github.com/gatsbyjs/gatsby-starter-hello-world

docs/tutorial/part-two/index.md

@@ -112,7 +112,7 @@ plugins.
 
 Let's start by creating a new site. At this point it probably makes sense to close the terminal windows you used to build tutorial-part-one so that you don't accidentally start building tutorial-part-two in the wrong place. If you don't close tutorial-part-one prior to building tutorial-part-two, you will see that tutorial-part-two appears at localhost:8001 instead of localhost:8000.
 
-Just like in part one, open a new terminal window and and run the following commands to create a new Gatsby site in a directory called `tutorial-part-two`. Then, change to this new directory:
+Just like in part one, open a new terminal window and run the following commands to create a new Gatsby site in a directory called `tutorial-part-two`. Then, change to this new directory:
 
 ```shell
 gatsby new tutorial-part-two https://github.com/gatsbyjs/gatsby-starter-hello-world