Fix dist import issue

[holgerd77]

Solution for #64

[michaelsbradleyjr]

Alternatively, you could keep this as dist/index.js, build from src/ into dist/, and place a script/s that doesn't get transpiled by babel at the top-level of the package, e.g. hdkey.js:

module.exports = require('./dist/hdkey.js');

For each module that people expect to be able to:

require('ethereumjs-wallet/<module>');

You would need a corresponding top-level script that's a one-liner re-export from the corresponding module in dist/.

[holgerd77]

Have re-triggered the tests after an update to the coveralls command since this was still failing.

[coveralls]

Coverage increased (+0.08%) to 88.462% when pulling b4c1c2e on fix-dist-import-issue into 71a51f1 on master.

[holgerd77]

Have looked at this again with a one-day-distance, will now merge since this is time-critical.