Update URL of community plugin repository

[drnextgis]

Fix for issue:

[warn]  ::::::::::::::::::::::::::::::::::::::::::::::
[warn]  ::          UNRESOLVED DEPENDENCIES         ::
[warn]  ::::::::::::::::::::::::::::::::::::::::::::::
[warn]  :: com.eed3si9n#sbt-assembly;0.7.3: not found
[warn]  ::::::::::::::::::::::::::::::::::::::::::::::
[warn] 
[warn]  Note: Some unresolved dependencies have extra attributes.  Check that these dependencies exist with the requested attributes.
[warn]      com.eed3si9n:sbt-assembly:0.7.3 (sbtVersion=0.11.2, scalaVersion=2.9.1)
[warn]