ARROW-4994: [Website] Update details for ptgoetz

Author: P. Taylor Goetz <tgoetz@monetate.com>

Closes #4009 from ptgoetz/ARROW-4994 and squashes the following commits:

83613d90 <P. Taylor Goetz> ARROW-4994: Update details for ptgoetz
diff --git a/committers.html b/committers.html
index d737250..f42af9d 100644
--- a/committers.html
+++ b/committers.html
@@ -39,7 +39,7 @@
 <td>P. Taylor Goetz</td>
 <td>PMC</td>
 <td>ptgoetz</td>
-<td>Hortonworks</td>
+<td>Monetate</td>
 </tr>
 <tr>
 <td>Julian Hyde</td>