Update patched versions for 2.5.X and 2.6.X+ series

As per comment mikel/mail#1097 (comment)
versions 2.5.5 and 2.6.6 include patches for this issue, 2.6.0 to 2.6.5 do not

mikel/mail 2-6-stable branch fixes in commit 37908c37dfb26ea262d0fa7916cd9bbee3750e63
mikel/mail 2-5-stable branch fixes in commit f4239e4cc03d982219a6fa58e059d8758bbd2d8f

Author: jeremyolliver

gems/mail/OSVDB-131677.yml

@@ -16,4 +16,5 @@ description: |
   Recipient Email Addresses." 2015. The attacks described in the paper (Terada,
   p. 4) can be applied to the library without any modification.
 patched_versions:
-- ">= 2.6.0"
+- "~> 2.5.5"
+- ">= 2.6.6"