title: Ngx-datatable header cell text are not vertically aligned
body: <p>i am using ngx-datatable in my angular project.
  Columns are ->  "Estimated Production Rate", "Wk1Rate", "WK2Rate", "WK3Rate". </p>
  
  <p>I applied Wrapping for text using css so that to accommodate text - "Estimated Production Rate" within the header cell.
  Thus, Estimated Production Rate is displayed in 3 lines, whereas other column names are displayed in single line.
  headerheight is 'auto', text-align for the header cells are "center"</p>
  
  <p>Problem - The texts - "Wk1Rate", "WK2Rate", "WK3Rate" - not vertically aligned within the header cell. these texts show at the top as shown in the image:</p>
  
  <p><a href="https://i.stack.imgur.com/LBhm0.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/LBhm0.png" alt="enter image description here"></a></p>
  
  <p>How can make these column to align vertically middle.? 
  i tried vertical-align:middle, but not working. Please help.</p>
  
  <p>html code for ngx-datatable:</p>
  
  <pre><code>    &lt;ngx-datatable class="material" [rows]="MyRows" [headerHeight]="'auto'" [footerHeight]="40"
       [rowHeight]="37" [limit]="10"&gt;
          &lt;ngx-datatable-column name="Est Production Rate" [sortable]="false" 
           [width]="85"&gt;
              &lt;ng-template ngx-datatable-cell-template let-value="value"&gt;
                  {{value}}
              &lt;/ng-template&gt;
          &lt;/ngx-datatable-column&gt;
          &lt;ngx-datatable-column name="Wk1Rate" [width]="80"&gt;
              &lt;ng-template ngx-datatable-cell-template let-value="value"&gt;
                  {{value}}
              &lt;/ng-template&gt;
          &lt;/ngx-datatable-column&gt;
  
          &lt;ngx-datatable-column name="Wk2Rate" [width]="80"&gt;
              &lt;ng-template ngx-datatable-cell-template let-value="value"&gt;
                  {{value}}
              &lt;/ng-template&gt;
          &lt;/ngx-datatable-column&gt;
  
          &lt;ngx-datatable-column name="Wk3Rate" [width]="80"&gt;
              &lt;ng-template ngx-datatable-cell-template let-value="value"&gt;
                  {{value}}
              &lt;/ng-template&gt;
          &lt;/ngx-datatable-column&gt;
      &lt;/ngx-datatable&gt;
  </code></pre>
  
  <p><a href="https://stackblitz.com/edit/angular-uakixj?file=src%2Fapp%2Fapp.component.html" rel="nofollow noreferrer">stackblitz</a> </p>