Update design_matrix.py
Merge pull request #324 from fabianp/patch-2

DOC: full list of HRF models accepted in make_dmtx
minor typos
do not execute non-executable, provide shebang for executable script
wip
Merge branch 'master' into motion_kalmann

* master:
  do not execute non-executable, provide shebang for executable script
  minor typos
  Update design_matrix.py