Read sbt.version in build.properties file

I have challenged the #9 task.
Tentatively, read build.properties at only project root directory.

I'm sorry but I'm not good at ShellScript,
so I hope you feel free to point out the bad points or reject it.

Current restriction ( or bug),
there are multiple lines settings in build.properties and
sbt.version's setting at second line or later,
version read will fail.