wiki pages: fix error when force renaming wiki page.

Bug: force renaming a wiki page fails. Fix: use the wiki page id instead
of the title in the update action.

test/system/wiki_pages_test.rb

@@ -0,0 +1,19 @@
+require "application_system_test_case"
+
+class WikiPagesTest < ApplicationSystemTestCase
+  context "renaming a wiki" do
+    should "work" do
+      @user = create(:user, level: User::Levels::BUILDER, created_at: 1.month.ago)
+      @wiki = as(@user) { create(:wiki_page, title: "kancolle") }
+
+      signin @user
+      visit wiki_page_path(@wiki)
+      click_on "Edit"
+      fill_in "Title", with: "kantai_collection"
+      click_on "Submit"
+
+      assert_selector "#wiki-page-title", text: "kantai collection"
+      assert_equal("kantai_collection", @wiki.reload.title)
+    end
+  end
+end