Fix the wrong chapter headers

ch22_vimrc.md

@@ -1,4 +1,4 @@
-# Ch21. Vimrc
+# Ch22. Vimrc
 
 In the previous chapters, you learned how to use Vim. In this chapter, you will learn how to organize and configure vimrc. 
 

ch23_vim_packages.md

@@ -1,4 +1,4 @@
-# Ch22. Vim Packages
+# Ch21. Vim Packages
 
 In the previous chapter, I mentioned using an external plugin manager to install plugins. Since version 8, Vim comes with its own built-in plugin manager called *packages*. In this chapter, you will learn how to use Vim packages to install plugins.
 

ch24_vim_runtime.md

@@ -1,4 +1,4 @@
-# Ch23. Vim Runtime
+# Ch24. Vim Runtime
 
 In the previous chapters, I mentioned that Vim automatically looks for special paths like `pack/` (Ch. 22) and `compiler/` (Ch. 19) inside the `~/.vim/` directory. These are examples of Vim runtime paths.
 

ch25_vimscript_basic_data_types.md

@@ -1,4 +1,4 @@
-# Ch24. Vimscript Basic Data Types
+# Ch25. Vimscript Basic Data Types
 
 In the next few chapters, you will learn about Vimscript, Vim's built-in programming language.
 

ch26_vimscript_conditionals_and_loops.md

@@ -1,4 +1,4 @@
-# Ch25. Vimscript Conditionals and Loops
+# Ch26. Vimscript Conditionals and Loops
 
 After learning what the basic data types are, the next step is to learn how to combine them together to start writing a basic program. A basic program consists of conditionals and loops.
 

ch27_vimscript_variable_scopes.md

@@ -1,4 +1,4 @@
-# Ch26. Vimscript Variable Scopes
+# Ch27. Vimscript Variable Scopes
 
 Before diving into Vimscript functions, let's learn about the different sources and scopes of Vim variables.
 

ch28_vimscript_functions.md

@@ -1,4 +1,4 @@
-# Ch27. Vimscript Functions
+# Ch28. Vimscript Functions
 
 Functions are means of abstraction, the third element in learning a new language.
 

ch29_plugin_example_writing-a-titlecase-plugin.md

@@ -1,4 +1,4 @@
-# Ch28. Write a Plugin: Creating a Titlecase Operator
+# Ch29. Write a Plugin: Creating a Titlecase Operator
 
 When you start to get good at Vim, you may want to write your own plugins. I recently wrote my first Vim plugin, [totitle-vim](https://github.com/iggredible/totitle-vim). It is a titlecase operator plugin, akin to Vim's uppercase `gU`, lowercase `gu`, and togglecase `g~` operators.