Use a better regular expression to find documented hooks in findHooks.php

Use a better regular expression to find documented hooks in findHooks.php

Added a ":" after the second quote so that only strings in the form
'Hook': are matched, otherwise the line 1172 of hooks.txt provoques the
the following message:
Documented and not found: value
because the line starts with 'value'.

Change-Id: I1d603e3fa10dcabf25e31f6a71aad233571738b5