Back button needs two clicks to go back

[thomask77]

While reporting Bug #387 , I noticed another problem:

• Your OS: Xubuntu 18.04
• Node.js version: v10.0.0
• VuePress version: 0.8.4
• Browser version: Firefox 59.0.2 (or chromium-browser 65.0.3325.181)
• Is this a global or local install: global
• Which package manager did you use for the install: npm

Steps to reproduce:

mkdir bug 
mkdir bug/subdir
cd bug

echo "# Link to [subdir](subdir)" > README.md
echo "# Subdirectory page" > subdir/README.md

vuepress dev

firefox http://localhost:8080    # same result with chromium-browser

• Click on "subdir"
• Click the browser's back button

Result:

• The first click only changes the browsers window title. Second click needed to go back.

Expected:

• Go back after the first click.