Update the updater to expect new names for the updater .jar files

We renamed a couple of components recently (in conjunction with a lot
of restructuring, including a move to the net.imagej.* packages). The
updater was unfortunately left behind, still thinking that the naming
convention is "ij-*.jar" instead of "imagej-*.jar".

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
Merge pull request #23 from imagej/new-jar-names

Update the updater to expect new names for the updater .jar files