regress: Update linear regression docs

JIRA: MADLIB-1460

As part of commit b0991965f7d4007d47902afcf7b319a78d766613 , we updated
num_rows_processed column to be of type BIGINT.  This commit makes the
doc changes for that code change

Authored-by: Ekta Khanna <ekhanna@vmware.com>
diff --git a/src/ports/postgres/modules/regress/linear.sql_in b/src/ports/postgres/modules/regress/linear.sql_in
index afc14d5..f767862 100644
--- a/src/ports/postgres/modules/regress/linear.sql_in
+++ b/src/ports/postgres/modules/regress/linear.sql_in
@@ -104,7 +104,7 @@
   </tr>
   <tr>
   <th>num_rows_processed</th>
-  <td>INTEGER. The number of rows that are actually used in each group.</td>
+  <td>BIGINT. The number of rows that are actually used in each group.</td>
   </tr>
   <tr>
   <th>num_missing_rows_skipped</th>