Fix table formatting

Author: shati-patel

docs/codeql/ql-language-reference/expressions.rst

@@ -533,14 +533,21 @@ The query produces these results:
 
 +-----------+---------+------+
 |  variant  | person  | cost |
-+-----------+---------+------+
++===========+=========+======+
 | default   | Alice   | 201  |
++-----------+---------+------+
 | default   | Bob     | 100  |
++-----------+---------+------+
 | default   | Charles | 100  |
++-----------+---------+------+
 | default   | Diane   | 0    |
++-----------+---------+------+
 | monotonic | Alice   | 101  |
++-----------+---------+------+
 | monotonic | Alice   | 200  |
++-----------+---------+------+
 | monotonic | Bob     | 100  |
++-----------+---------+------+
 | monotonic | Diane   | 0    |
 +-----------+---------+------+