Bug in the Theme Inheritance docs, when the installation is done cloning Grav from github

**Do you want to request a *feature* or report a *bug*?**

I'm reporting a bug in the documentation: the current procedure does not produce the intended result _when the installation is done cloning Grav from github_

**What is the current behavior?**

Upon finishing [Theme Inheritance](https://learn.getgrav.org/themes/customization#theme-inheritance) and [Easy Theme Development with Inheritance](https://getgrav.org/blog/theme-development-with-inheritance) many times on a clean installation of GravCMS I always get `RuntimeException (400) Template "default.html.twig" is not defined.`

**If the current behavior is a bug, please provide the steps to reproduce and if possible a minimal demo of the problem**

1. Clean installation of gravCMS cloning from GIT (Amazon Cloud Services failed that day)
1. Installed DevTools using the CLI
1. Carefully followed the instructions in [Theme Inheritance](https://learn.getgrav.org/themes/customization#theme-inheritance) and then erased the resulting theme and tried again with [Easy Theme Development with Inheritance](https://getgrav.org/blog/theme-development-with-inheritance)
1. I got `RuntimeException (400) Template "default.html.twig" is not defined.` both times.

The solution was to copy the default template to the new theme, but that's not the way it is supposed to work

**What is the expected behavior?**

>You have now created a new theme called mytheme and set up the streams so that it will first look in the mytheme theme first, then try antimatter. So in essence, Antimatter is the base-theme for this new theme.

I was expecting to be able to use any of the templates in antimatter and changing just the CSS in the new theme

**Which versions of OS are affected by this issue? Did this work in previous versions?**

I was using Grav v1.1.17 - Admin v1.2.14 - on OSX "El Capitán", cloned form GitHUB

**This only happened when cloning form GitHub**, afterwards I downloaded the whole package as usual and it worked as described in the docs.

Start by comparing the Theme Inheritance documentation and the Easy Theme Development with Inheritance blog instructions, then reproduce the reported error using a Grav installation cloned from GitHub. Done means the documented procedure works without copying the default template and explains any difference from the downloaded package.

Written by the indexing model from the issue text.