Javascript changes: API changes

[hzoo]

Things in https://github.com/babel/notes/issues/30. Related to https://github.com/babel/babel-upgrade/issues/39

Example:

- file.delete('espowerAssertionVisitor');
+ file.set('espowerAssertionVisitor', null);

[twada]

https://github.com/power-assert-js/babel-plugin-espower/pull/23/commits/89a9d7e998f5c708429d56ee3a6a01cbbee5cb3c file.opts.parserOpts instead of file.parserOpts

[twada]

https://github.com/power-assert-js/babel-plugin-espower/pull/23/commits/ff72e23275996d69e5ed72f3c6f9cdaa05e0159c use file.inputMap to handle incoming sourcemaps (file.opts.inputSourceMap has gone away)