Replace PNG logo with SVG logo

Author: gakimball

README.md

@@ -1,5 +1,5 @@
 <h1 align="center">
-  <img width="400" src="https://raw.githubusercontent.com/gakimball/ocha/master/assets/logo.svg" alt="Ocha">
+  <img width="400" src="https://raw.githubusercontent.com/gakimball/ocha/master/assets/logo.png" alt="Ocha">
 </h1>
 
 A BDD-style assertion library for Sass. Eventually it will maybe work with [True](https://github.com/oddbird/true).