Fix a bug where the manifest is missing its last line.

Despite the documentation on java.util.jar.Manifest [1], the Manifest class
seems to require an endline in its input. If not, it drops the last line (on my
system, version [2], anyway).

[1] http://docs.oracle.com/javase/6/docs/technotes/guides/jar/jar.html
[2] $ java -version
java version "1.7.0_21"
OpenJDK Runtime Environment (IcedTea 2.3.9) (7u21-2.3.9-0ubuntu0.12.04.1)
OpenJDK 64-Bit Server VM (build 23.7-b01, mixed mode)