Update test script to compile test files with elm-make before and after formatting

[avh4]

This only needs to be done for the test files that are compatible with the latest version of Elm.

[Janiczek]

I just want to be sure I understand correctly before trying anything:

Do we compare the two generated .js files and want them to be the same?

Do we FAIL the tests if

• the file is not valid before formatting (elm-make throws error)
• the file is valid before but not valid after formatting (elm-make throws error)
• the afterFormatting.js file is not the same as original.js (diff shows something)

and SUCCESS otherwise?

[Janiczek]

@avh4 bump... :) could you please just clarify? I can then try to do this.

[avh4]

Failing if elm-make fails before or after is the most important.

I hadn't thought of comparing the js. That sounds like it could be useful, though I'm not 100% certain that the js will never change because of formatting. I think the comparison would be good to have, but it's less important than just making sure elm-make can still parse the file.