update collaborators file

collaborators.md

@@ -8,4 +8,5 @@ dat is only possible due to the excellent work of the following collaborators:
<tr><th align="left">bmpvieira</th><td><a href="https://github.com/bmpvieira">GitHub/bmpvieira</a></td></tr>
<tr><th align="left">waldoj</th><td><a href="https://github.com/waldoj">GitHub/waldoj</a></td></tr>
<tr><th align="left">pkafei</th><td><a href="https://github.com/pkafei">GitHub/pkafei</a></td></tr>
<tr><th align="left">karissa</th><td><a href="https://github.com/karissa">GitHub/karissa</a></td></tr>
</tbody></table>