adding drop shadow styling to image in episode 3 to improve legibility in the lesson

Author: emcaulay

_episodes/03-sharing.md

@@ -36,7 +36,7 @@ Clicking `New Repository` will take you to a creation page with different option
 
 * Name your repository "hello-world."
 
-![The 'create a new repository' form on GitHub](../fig/github-repo-new-setup.png) 
+![The 'create a new repository' form on GitHub](../fig/github-repo-new-setup.png){: .image-with-shadow } 
 
 GitHub will ask if you want to add a README.md, license or a `.gitignore` file. Do not do any of that for now -- We want you to start with a completely empty repository on GitHub.