Update promises_aplus_tests dependency

[dudaerich]

promises_aplus_tests does not exist anymore.
Now its name is promises-aplus-tests.

This closes #701

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[dudaerich]

I signed it!

[googlebot]

CLAs look good, thanks!

[jkevingutierrez]

Any updates on this?

[shicks]

We have some difficulty actually accepting changes to package.json. But this looks fine, so I'll merge it here and we can deal with reconciling it internally later.