title: How to remove background ripple effect from custom action button in material-table?
body: <p>I want to remove the background ripple effect from the custom buttons I have created in the toolbar in place of default icon buttons.
  Refer to screenshot below, I want to remove the ripple effect (the circle one) only from import and add buttons, all other action icon buttons should behave normally.</p>
  
  <p><img src="https://i.ibb.co/rF182CP/Screenshot-from-2019-04-25-12-02-52.png" alt="table screenshot"></p>
  
  <pre><code>                    &lt;MaterialTable
                          columns={columns}
                          data={this.state.data}
                          icons={{
                              Add:()=&gt;&lt;AddTaskButton onClick={()=&gt;{}}/&gt;
                          }}
                          actions={[
                              {
                                  icon:this.renderImportButton,
                                  isFreeAction:true
                              }
                          ]}
                          editable={{
                              onRowAdd: newData =&gt; this.onRowAdd(newData)
                          }}
                      /&gt;
  </code></pre>