Dashboard, after login use relative url. (#4103)

esphome/dashboard/dashboard.py

@@ -842,7 +842,7 @@ PING_REQUEST = threading.Event()
 class LoginHandler(BaseHandler):
     def get(self):
         if is_authenticated(self):
-            self.redirect("/")
+            self.redirect("./")
         else:
             self.render_login_page()
 
@@ -887,7 +887,7 @@ class LoginHandler(BaseHandler):
         password = self.get_argument("password", "")
         if settings.check_password(username, password):
             self.set_secure_cookie("authenticated", cookie_authenticated_yes)
-            self.redirect("/")
+            self.redirect("./")
             return
         error_str = (
             "Invalid username or password" if settings.username else "Invalid password"