Docs: Fix Introduction -> Version history table format

Updated the docs/introduction/readme.rst file to generate
correct html format for version history.

Change-Id: Ief1e413dbb6b49ad9bb57a129f395cea9f2c8f64
Signed-off-by: Maulik Patel <maulik.patel@arm.com>
diff --git a/docs/introduction/readme.rst b/docs/introduction/readme.rst
index 2e07c11..6f3da4c 100644
--- a/docs/introduction/readme.rst
+++ b/docs/introduction/readme.rst
@@ -190,7 +190,7 @@
 | v1.0        | 2020-03-27   | 1.0 release        | v20.03_API1.0     |
 +-------------+--------------+--------------------+-------------------+
 | v1.1        | 2020-07-15   | 1.1 release        | 1f960947          |
-+---------------------------------------------------------------------+
++-------------+--------------+--------------------+-------------------+
 | v1.2.0      | 2020-11-25   | 1.2.0 release      | 90c8e680          |
 +-------------+--------------+--------------------+-------------------+