Include Apple IST CA 8 - G1 in the list of Symantec sub-CAs exempt from CT

This was merely a documentation issue; the actual CA was included within
the //net/data/ssl/symantec/excluded directory, and properly excluded by
//net/http/transport_security_state_ct_policies.inc, but the README file
unintentionally omitted it.

BUG=none
R=davidben@chromium.org

Change-Id: I62426618cfa58ad392a94999c4db71f22f70b1c3
Reviewed-on: https://chromium-review.googlesource.com/569003
Commit-Queue: Ryan Sleevi <rsleevi@chromium.org>
Reviewed-by: David Benjamin <davidben@chromium.org>
Reviewed-by: Ryan Sleevi <rsleevi@chromium.org>
Cr-Commit-Position: refs/heads/master@{#488714}

net/data/ssl/symantec/README.md

@@ -32,6 +32,7 @@ The following command can be used to match certificates and their key hashes:
   * [6115f06a338a649e61585210e76f2ece3989bca65a62b066040cd7c5f408edd0.pem](excluded/6115f06a338a649e61585210e76f2ece3989bca65a62b066040cd7c5f408edd0.pem)
   * [904fb5a437754b1b32b80ebae7416db63d05f56a9939720b7c8e3dcc54f6a3d1.pem](excluded/904fb5a437754b1b32b80ebae7416db63d05f56a9939720b7c8e3dcc54f6a3d1.pem)
   * [ac2b922ecfd5e01711772fea8ed372de9d1e2245fce3f57a9cdbec77296a424b.pem](excluded/ac2b922ecfd5e01711772fea8ed372de9d1e2245fce3f57a9cdbec77296a424b.pem)
+  * [a4fe7c7f15155f3f0aef7aaa83cf6e06deb97ca3f909df920ac1490882d488ed.pem](excluded/a4fe7c7f15155f3f0aef7aaa83cf6e06deb97ca3f909df920ac1490882d488ed.pem)
 
 ### Google