Use constant for SNAPSHOT

Author: grrowl

src/index.js

@@ -1,4 +1,5 @@
 import Dispatcher from './dispatcher'
+import { UPDATE_SNAPSHOT } from './constants'
 
 export { isGossipType } from './dispatcher'
 export {
@@ -138,4 +139,4 @@ function connectStreams(io, createStream) {
 // devToolsStateSanitizer can be applied to the devToolsExtension
 // as the stateSanitizer to show correctly the store state instead
 // of showing the internal representation of redux-scuttlebutt
-export const devToolsStateSanitizer = (state) => state.slice(-1)[0][3]
+export const devToolsStateSanitizer = (state) => state.slice(-1)[0][UPDATE_SNAPSHOT]