update to fontawesome 4

[bootswatch] / bower_components / font-awesome / src / assets / less / site / bootstrap / buttons.less

.btn { box-shadow: inset 0 1px 0 rgba(255,255,255,0.2); }
.btn-default { text-shadow: 0 1px 0 #fff; }
.btn-primary, .btn-success, .btn-warning, .btn-danger, .btn-info { text-shadow: 0 1px 0 rgba(0,0,0,0.2); }