Text in <th>/<td> ignore default alignment

Table (header) cells lose default alignment because Bootstrap by default enforces:

.table th,
.table td {
  padding: 8px;
  line-height: 20px;
  text-align: left;
  vertical-align: top;
  border-top: 1px solid #dddddd;
} 

We need to revert it and not enfore any alignment otherwise <th> elements aren't centered anymore.