Add the filename to ejs for `include` directive

EJS has a newer `include` directive to replace the old `partial` function in express. This just includes a file relative to the current. The engine has to know the path of the template in order for this to happen.
Merge pull request #59 from CamShaft/patch-2

Add the filename to ejs for `include` directive
Merge branch 'master' of https://github.com/nodeca/mincer

* 'master' of https://github.com/nodeca/mincer:
  Add the filename to ejs for `include` directive