Full URL to quicktype logo in README

The logo didn't display on NPM with a relative URL
2018-04-29 20:51:01 -07:00 · 2018-04-29 20:51:01 -07:00 · 49954657ce
--- a/README.md
+++ b/README.md
@ -1,4 +1,4 @@
-![](quicktype-logo.svg)
+![](https://raw.githubusercontent.com/quicktype/quicktype/master/quicktype-logo.svg?sanitize=true)

 [![npm version](https://badge.fury.io/js/quicktype.svg)](https://badge.fury.io/js/quicktype)
 [![Build status](https://badge.buildkite.com/147309f9f492c2af1ea53df922be7140ba4035dbb31f61ee1e.svg)](https://buildkite.com/typeguard/quicktype-master)