BUG: incorrect dimensions for surfaceTensionForce

- accidentally introduced by 59ae80c5

STYLE: trial use of brace-initialized dimensionSet

- instead of writing

      dimensionedScalar(dimensionSet(1, -2, -2, 0, 0, 0), Zero);

  we can use C++11 brace-initialization to bundle the parameters
  for the dimensionSet construction and simply write

      dimensionedScalar({1, -2, -2, 0, 0, 0}, Zero);

  Note the following is incorrect syntax (extra brackets):

      dimensionedScalar(({1, -2, -2, 0, 0, 0}), Zero);