Changing The Apache Default MIME Type
If you have web pages without any file extension, then Apache will, by default, send the wrong MIME type to your browser and you'll end up seeing the HTML rather than the rendered page. By changing the default MIME type, you can resolve this problem.
At the Pi command line, edit the Apache configuration file apache2.conf.
sudo nano /etc/apache2/apache2.conf
Now locate the DefaultType statement and change its value from text/plain to text/html. Restart the Apache server.
sudo /etc/init.d/apache2 reload