Fix duplicate movement test case

* inst/tests/test-trace.R: The duplicate movement test case have been
  fixed. The failure was due to an error when sorting the data.frame,
  the code erronously ordered the sequence 1:6 instead of the first 6
  columns in the data.frame
Updated NEWS
Bumbed version to 0.8.8

* DESCRIPTION: Updated version to 0.8.8. Updated R dependance to
  R(>=3.0.0)