removed phantomjs dependency

[akmorrow13]

No description provided.

[akmorrow13]

Addresses #517 and #503

[akmorrow13]

TODOs:

• Test with node 12.0.0

• fix coverage

[coveralls]

Coverage increased (+0.03%) to 91.456% when pulling f740cbf on akmorrow13:remove_phantomjs into 86a841b on hammerlab:master.

[akmorrow13]

ping @piotr-gawron maybe this will fix issue #517

[piotr-gawron]

Dear @akmorrow13,
I checked it and it works fine: everything installed without problem and all tests are green (checked on both 12.0.0 and 10.15.3).

Since you decided to remove deprecated phantomejs do you also plan to upgrade other libraries? simple

npm audit

reports found 42 vulnerabilities (9 low, 22 moderate, 10 high, 1 critical) in the dependencies...

[akmorrow13]

Thanks for testing @piotr-gawron! Removing and replacing some of these libraries broke different aspects of pileup.js, so I will not be addressing them here. PRs for fixes are always welcome, however!