plumbing: object, correct tag PGP encoding
plumbing: object, correct tag PGP encoding

As with the update in ec3d2a8, tag encoding needed to be corrected to
ensure extra newlines were not being added in during tag object
encoding, so that it did not corrupt the object for verification.

Signed-off-by: Chris Marchesi <1559339698d4b91062141e6c67af7c94ca1d6f09@vancluevertech.com>

go-git/go-git,src-d/go-git,go-git/go-git,mcuadros/go-git,src-d/go-git,mcuadros/go-git