Updated Readme Logo (#4701)

* clean up svg logo source

* try raw link

* try rawgit link

* add logo width

README.md

@@ -1,4 +1,4 @@
-<img src="http://leafletjs.com/docs/images/logo.png" alt="Leaflet" />
+<img width="600" src="https://rawgit.com/Leaflet/Leaflet/logo/src/images/logo.svg" alt="Leaflet" />
 
 Leaflet is the leading open-source JavaScript library for **mobile-friendly interactive maps**.
 Weighing just about 33 KB of gzipped JS code, it has all the mapping [features][] most developers ever need.