upgrade to sbt 0.13.7

it's what the cool kids are using

safer to keep the blank lines in our *.sbt files for now though
Merge pull request #116 from NetLogo/sbt-0.13.7

upgrade to sbt 0.13.7
Update NetLogo-Headless
Revert "Disabling dependency permissioning in these pastures..."

This reverts commit 75ef923cfa8213511ed5b5bdc82c2db9ae244df9.
Getting the dependency checker running again
Reworking links for speed, structure, and proper ordering
Testing Virus on a Network
Sanitizing single quotes in single-quoted JS strings
Correctly computing link equality with `nobody`
Updating infrastructure in wake of previous commit

  * Updating Headless artifact to include a language test that would have caught this bug
  * Adding "PageRank" model to set of model tests, since it caught the bug and now runs correctly
  * Adding model dump for "PageRank"
Updating NetLogo-Headless
remove unused dependency