Fix failing CI checks for GNU Emacs 25

[mtreca]

CI checks for GNU Emacs 25 keep failing.

@conao3 is there anything we can do to fix these?

[conao3]

Yes it is my fault but I cannot understand why.

[mtreca]

No worries, I will try to look into it today.

I replaced the Cask call with the native make test in my fork (see here) and I have contrasting results:

• The ERT test failures are not picked up as failures, but the tests are now running properly (I had to fix the Makefile for this, see commit 5fd785c47570687661cd850e64b8f363d6c88b2d).
• I have issues in GNU Emacs 24 and 25 (caddr is not recognized for some reasons). EDIT: Fixed this issue by requiring cl before running tests.

Should we push those changes and maybe remove the Cask setup until we write some proper tests for the package? Next step would be to make the Github CI runner recognize failing ERT tests (we will have to fix them later on, I opened an issue about it in #70).

[mtreca]

Fixed in 1dd661e