Run ``make specs`` on Circle/Travis

[oesteban]

Summary

The idea is to free devs and contributors from running make specs.

One build (maybe a lighter one with few dependencies) runs make specs and stores the git diff as an artifact that should be reviewed before merging in a PR.

Then, merge commits have a special section after make specs were the updated specs are committed and pushed back to master automatically.

[effigies]

A simple Travis job:

make specs
git add nipype
[ "$( git diff --cached | wc -l )" -eq 0 ] || ( git diff --cached && false )

You could also do make check-before-commit in place of calling pytest directly, and that will catch tests that pollute the repository, as well.

[effigies]

I'm a little hesitant to give CI the ability to push to the repository.