Pin templates to specific versions

Related to #14

This is so that if people read older drafts of the book the examples
continue to work and match the text for those drafts

Author: Gabriella439

manuscript/Setup.md

@@ -199,7 +199,7 @@ If you are using Linux (including NixOS or the Windows Subsystem for Linux) you
 Run the following command to generate your first project:
 
 ```bash
-$ nix flake init --template 'github:Gabriella439/nixos-in-production#setup'
+$ nix flake init --template 'github:Gabriella439/nixos-in-production/0.4#setup'
 ```
 
 … that will generate the following `flake.nix` file:

manuscript/Terraform.md

@@ -47,7 +47,7 @@ the list of [AWS service endpoints](https://docs.aws.amazon.com/general/latest/g
 Now run the following command to bootstrap our first Terraform project:
 
 ```bash
-$ nix flake init --template 'github:Gabriella439/nixos-in-production#terraform'
+$ nix flake init --template 'github:Gabriella439/nixos-in-production/0.4#terraform'
 ```
 
 … which will generate the following files:

manuscript/WebServer.md

@@ -7,13 +7,13 @@ Now that we can build and run a local NixOS virtual machine we can create our fi
 We'll begin from the template project from "Setting up your development environment".  You can either begin from the previous chapter by running the following command (if you haven't done so already):
 
 ```bash
-$ nix flake init --template 'github:Gabriella439/nixos-in-production#setup'
+$ nix flake init --template 'github:Gabriella439/nixos-in-production/0.4#setup'
 ```
 
 … or if you want to skip straight to the final result at the end of this chapter you can run:
 
 ```bash
-$ nix flake init --template 'github:Gabriella439/nixos-in-production#server'
+$ nix flake init --template 'github:Gabriella439/nixos-in-production/0.4#server'
 ```
 
 Let's modify `module.nix` to specify a machine that serves a simple static "Hello, world!" page on `http://localhost`: