Fix bootstrap css class for buttons in index.php view

Signed-off-by: Maxime Buquet <m.buquet@willdo.co.jp>
Merge pull request #234 from Ppjet6/view_index_btn_class

Fix bootstrap css class for buttons in index.php view
Merge branch '1.8/develop' of https://github.com/fuel/oil into 1.8/develop