Fix overwriting of dynamic import() CallExpression

[vikr01]

Closes #1035
Closes #1166

So turns out, dynamic imports were already supported in moduleVisitor but they were being overwritten if commonjs or amd options were set.

• Fixed by saving the current CallExpression and including it in the function that's overwriting it.
• Added test cases for import() in rules using the moduleVisitor. Not sure why, but I couldn't get the no-cycle rule to throw errors with import().
• Fixes issues with parser babel-eslint not working with no-cycle, due to the "flow workaround" for eslint@<5

This might be breaking for some users, though.

Also since import() can work with URLs, maybe we should use something like isURL from validator to ignore URL imports?

[coveralls]

Coverage decreased (-0.002%) to 97.863% when pulling 70a59fe on vikr01:fix/dynamic-import into e4850df on benmosher:master.

[coveralls]

Coverage increased (+0.09%) to 97.349% when pulling 19f7442 on vikr01:fix/dynamic-import into b4a2f11 on benmosher:master.

[edmorley]

@ljharb thank you for reviewing this and the related #1231.
Do we need a second reviewer, if so, who is best to ask? :-)

[benmosher]

looks great, thanks! need to re-run tests for this after #1254 lands but otherwise LGTM!

[corradio]

any updates here? Would be great to have this merged