Create tmp files with .browserify.js extension

[etpinard]

... instead of .browserify to avoid "Invalid file type" logs in karma@3.1.1 from a patch added in karma-runner/karma#3165

Before 4ef50af

npm test > npm-test.base.txt
grep Invalid npm-test.base.txt

# gives
30 11 2018 15:42:10.544:WARN [middleware:karma]: Invalid file type, defaulting to js. browserify
30 11 2018 15:42:30.195:WARN [middleware:karma]: Invalid file type, defaulting to js. browserify
30 11 2018 15:42:31.145:WARN [middleware:karma]: Invalid file type, defaulting to js. browserify

and after

npm test > npm-test.txt
grep Invalid npm-test.txt
# blank!

npm-test.base.txt
npm-test.txt

I could of course add a test for this, if deemed necessary.

[etpinard]

Ah. Looks like karma@3 dropped support for Node@4.

I should probably revert aff7a53, unless karma-browserify is ok with dropping Node@4 support.

Edit: [...] is ok with not being tested on Node@4.

[bendrucker]

I think it would be ok to drop Node 4 support as part of karma@3 compatibility. It's almost certainly more important to test on karma@latest than continue to support karma@2.

[bendrucker]

If anything a "no WARN logs are printed" test could be nice. If that's too tricky no test against this change is ok too.

[etpinard]

@bendrucker thanks for taking a look at my PR!

I should be able to add a test at some point next week.

[bendrucker]

Cool! Test is far from required and could even be submitted separately. I would be ok merging this now with:

• node@4 removed from Travis
• peerDependencies.karma updated
• engines.node updated

[bendrucker]

Thanks! Published as a major (because of the peer + node version changes).