fix(html5): make base case insensitive

Fix #2154

This is mostly convenience so it's always made case insensitive. If there are
any case sensitive requirements, the test should be made server side.

src/history/html5.js

@@ -73,7 +73,7 @@ export class HTML5History extends History {
 
 export function getLocation (base: string): string {
   let path = decodeURI(window.location.pathname)
-  if (base && path.indexOf(base) === 0) {
+  if (base && path.toLowerCase().indexOf(base.toLowerCase()) === 0) {
     path = path.slice(base.length)
   }
   return (path || '/') + window.location.search + window.location.hash