corporate_identity: fix markup in table of content

There was opening and closing tags mismatch:
    <div><a href="#references1_anchor">References</div></a>
6 jobs for fix/corporate_identity_div_a in 0 seconds
Status Job ID Name Coverage
  External
passed ERP5.CodingStyleTest-TestRunner1

01:59:47

passed ERP5.PerformanceTest-TestRunner1

00:25:38

failed ERP5.UnitTest-TestRunner1

02:25:07

passed ERP5.CodingStyleTest-TestRunner1

00:26:26

passed ERP5.PerformanceTest-TestRunner1

00:25:52

failed ERP5.UnitTest-TestRunner1

01:03:40