Log Message:
gmime3: update to 3.2.6.

### GMime 3.2.6

* Added methods to get 64-bit timestamps for the creation-date and expiration-date of
  GMimeCertificates and GMimeSignatures. (issue #68)

* Fixed the vala abstract public constructor for GMimeObject. (issue #76)

* Fixed a bug in GMimeParser's header parser. (issue #78)

* Added build files for Visual Studio 2017 thanks to Vitaliy Didik.