insert newline between concatenated files

[plasmagunman]

some files have a "//"-style comment in their last line and don't have a newline at EOF, when concatenating them, the first line of the next file will end up in the comment.

to be on the safe side bowerful could add add a "\n" at the end of each file.

to reproduce use bowerfull with

packages: {
  'wavesurfer.js': '0.2.3',
  vis: '3.3.0',
},

will lead to a parsing error, no matter the order.