gitx-rowanj: Version and checksum

According to #1021, versioned/checksummed downloads should be preferred
when available and the URL contains the version number. This is the case
with gitx-rowanj—in fact, the appcast referenced links to the versioned
downloads, not the unversioned one.
Merge pull request #6126 from treyharris/gitx-rowanj

gitx-rowanj: Version and checksum