Properties with underscores in their name cannot be indexed

Steps to reproduce

1. create a model with a property name that contains an underscore in it (e.g. short_name).
2. set that property to be indexed (e.g. "index": true)
3. call pg.autoupdate() (e.g. where app.datasources.pg);

Current Behavior

1. The index is added
2. Then the index is dropped

Expected Behavior

1. The index is added

Additional information

The bug shown here is a bad regular expression in migration.js (on or about line 777):
const propNameRegEx = new RegExp('^' + self.table(model) + '_([^_]+)_idx');

The simple fix is:
const propNameRegEx = new RegExp('^' + self.table(model) + '_(.*)(?:_idx)$');

Start in migration.js around line 777 and reproduce the reported model setup with an underscored property, then call pg.autoupdate(). Verify that the existing index remains after migration and that the property name is matched correctly when it contains underscores.