updated matrix.js

added:
- vectorNorm, which calculates different norms of a vector;
- matrixNorm, which calculates different norms of a matrix;
- isUpperBand, which determines if a matrix is of an upper bandwidth;
- isLowerBand, which determines if a matrix is of a lower bandwidth

also updated the .travis.yml file so we can test with Node 0.10.x
add brackets for consistency