Fix wrong formatting for URL that ends with /

Author: Alexis Boissonnat

tea-cup/src/TeaCup/Navigation.test.ts

@@ -97,6 +97,7 @@ const router: Router<MyRoute> = new Router(
 
 expectRoute('/', home());
 expectRoute('/songs', songs(nothing));
+expectRoute('/songs/', songs(nothing));
 expectRoute('/song/123', song(123));
 expectRoute('/song/123/edit', song(123, true));
 expectRoute('/songs?q=foobar', songs(just('foobar')));

tea-cup/src/TeaCup/Navigation.tsx

@@ -331,7 +331,7 @@ export class RouteDef<R> implements RouteBase<R> {
 
   static sanitizePath(path: string): string {
     const p1 = path.startsWith('/') ? path.substring(1) : path;
-    return p1.endsWith('/') ? p1.substring(0, p1.length - 2) : p1;
+    return p1.endsWith('/') ? p1.substring(0, p1.length - 1) : p1;
   }
 
   static splitPath(path: string): ReadonlyArray<string> {