Fix VS 2017 svg ref per README.md ref

sourcetree-macos-tutorial.md

@@ -138,7 +138,7 @@ Now let's get you started with contributing to other projects. We've compiled a
 
 ## Tutorials Using Other Tools
 
-|<a href="github-desktop-tutorial.md"><img alt="GitHub Desktop" src="https://desktop.github.com/images/desktop-icon.svg" width="100"></a>|<a href="github-windows-vs2017-tutorial.md"><img alt="Visual Studio 2017" src="https://www.visualstudio.com/wp-content/uploads/2017/11/microsoft-visual-studio.svg" width="100"></a>|<a href="gitkraken-tutorial.md"><img alt="GitKraken" src="/assets/gk-icon.png" width="100"></a>|<a href="github-windows-vs-code-tutorial.md"><img alt="VS Code" src="https://upload.wikimedia.org/wikipedia/commons/2/2d/Visual_Studio_Code_1.18_icon.svg" width=100></a>|<a href="sourcetree-macos-tutorial.md"><img alt="Sourcetree App" src="https://wac-cdn.atlassian.com/dam/jcr:81b15cde-be2e-4f4a-8af7-9436f4a1b431/Sourcetree-icon-blue.svg" width=100></a>|
+|<a href="github-desktop-tutorial.md"><img alt="GitHub Desktop" src="https://desktop.github.com/images/desktop-icon.svg" width="100"></a>|<a href="github-windows-vs2017-tutorial.md"><img alt="Visual Studio 2017" src="https://upload.wikimedia.org/wikipedia/commons/c/cd/Visual_Studio_2017_Logo.svg" width="100"></a>|<a href="gitkraken-tutorial.md"><img alt="GitKraken" src="/assets/gk-icon.png" width="100"></a>|<a href="github-windows-vs-code-tutorial.md"><img alt="VS Code" src="https://upload.wikimedia.org/wikipedia/commons/2/2d/Visual_Studio_Code_1.18_icon.svg" width=100></a>|<a href="sourcetree-macos-tutorial.md"><img alt="Sourcetree App" src="https://wac-cdn.atlassian.com/dam/jcr:81b15cde-be2e-4f4a-8af7-9436f4a1b431/Sourcetree-icon-blue.svg" width=100></a>|
 |---|---|---|---|---|
 |[GitHub Desktop](github-desktop-tutorial.md)|[Visual Studio 2017](github-windows-vs2017-tutorial.md)|[GitKraken](gitkraken-tutorial.md)|[Visual Studio Code](github-windows-vs-code-tutorial.md)|[Atlassian Sourcetree](sourcetree-macos-tutorial.md)|