Source maps stopped populating names in 6to5@1.7.0

[es128]

Source map from 1.6.0:

{"version":3,"sources":["fixture.js"],"names":["Test"],"mappings":"IAAMA,I;WAAAA,I;;SAAAA,I","file":"fixture.js","sourcesContent":["class Test {}\n"]}

Source map from 1.7.0:

{"version":3,"file":"fixture.js","sources":["fixture.js"],"names":[],"mappings":"IAAM,CAAC,CAAC,CAAC;WAAH,CAAC,CAAC,CAAC;SAAH,CAAC,CAAC,CAAC","sourcesContent":["class Test {}\n"]}

Appears to be a side effect from the switch to recast. Might not be important, but I figured I'd report it.

[sebmck]

I've added more reliable source map tests with commit d511fc8. Hopefully this catches all future source map issues.