Bump component versions

The following changes were made:
	imagej-legacy.version = 0.5.19 (latest net.imagej:imagej-legacy)
	imagej-updater.version = 0.4.2 (latest net.imagej:imagej-updater)

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
Bump ImageJ release candidate version preemptively

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>