Smarttable with selectmode as multi

### Issue type

**I'm submitting a ...** (check one with "x")

* [x ] bug report
* [ ] feature request
* [ ] question about the decisions made in the repository

### Issue description

**Current behavior:**
In latest code ,in smarttable when selectmode="multi",it show checkbox ,but the size of checkbox is large.

**Expected behavior:**
the size of checkbox should be same as header in the table.