Fix Auto Update entry for ELK

[csnyulas]

The current update.properties file for the ELK reasoner plugin that is listed in Protege 5.5 plugin repository (http://elk.semanticweb.org/maven/latest/elk-distribution/resources/p5.update.properties) is unreachable, and gives a "Connection timed out" error. This causes a long delay before Protege shows the window with the available plug-in versions whenever a "Check for plugins..." action is executed.

There was an issue filed for this on the ELK repository, which provides more details, and potential solutions: liveontologies/elk-reasoner#58

Depending on how that issue will be resolved, we should fix the ELK entry in the plugins.repository file.

[matthewhorridge]

Temporary workaround in place now