Fix invalid private repository SVG image URLs

SVG images like the repository hero were not rendered because they used
the URLs for public repositories instead of the ones that allow to
resolve the files in private repositories:

```diff
-https://raw.githubusercontent.com/svengreb/tmpl/master/assets/images/repository-hero.svg?sanitize=true
+https://github.com/svengreb/tmpl/blob/master/assets/images/repository-hero.svg?raw=true
```

GH-21

README.md

@@ -1,4 +1,4 @@
-<p align="center"><img src="https://raw.githubusercontent.com/svengreb/tmpl/master/assets/images/repository-hero.svg?sanitize=true"/></p>
+<p align="center"><img src="https://github.com/svengreb/tmpl/blob/master/assets/images/repository-hero.svg?raw=true"/></p>
 
 <p align="center"><a href="https://github.com/svengreb/tmpl/releases/latest"><img src="https://img.shields.io/github/release/svengreb/tmpl.svg?style=flat-square&label=Release&logo=github&logoColor=eceff4&colorA=4c566a&colorB=88c0d0"/></a> <a href="https://github.com/svengreb/tmpl/blob/master/CHANGELOG.md"><img src="https://img.shields.io/github/release/svengreb/tmpl.svg?style=flat-square&label=Changelog&logo=github&logoColor=eceff4&colorA=4c566a&colorB=88c0d0"/></a></p>