message: Update README.md
  Fixed doi links 3 & 4
diff: @@ -22,9 +22,9 @@ Kennedy, G. J. and Martins, J. R. R. A, "A parallel finite-element framework for
  These papers describe in detail the aggregation functional implementation in TACS:
  -Kennedy, G. J. and Hicken, J. E., "Improved Constraint-Aggregation Methods", Computer Methods in Applied Mechanics and Engineering, 2015, doi:10.1016/j.cma.2015.02.017
  +Kennedy, G. J. and Hicken, J. E., "Improved Constraint-Aggregation Methods", Computer Methods in Applied Mechanics and Engineering, 2015, doi:http://dx.doi.org/10.1016/j.cma.2015.02.017
  -Kennedy, G. J., "Strategies for adaptive optimization with aggregation constraints using interior-point methods", 2015, doi:10.1016/j.compstruc.2015.02.024
  +Kennedy, G. J., "Strategies for adaptive optimization with aggregation constraints using interior-point methods", 2015, doi:http://dx.doi.org/10.1016/j.compstruc.2015.02.024
  # Setting up and installing TACS #
  