Invalid regular expression

I get the following error when trying to use the CLI. Note that I've elided the full regex (which is very long)

```
$ write-good
/usr/local/lib/node_modules/write-good/node_modules/too-wordy/too-wordy.js:244
const wordyRegex = new RegExp(`\\b(?)
at Object. (/usr/local/lib/node_modules/write-good/node_modules/too-wordy/too-wordy.js:244:20)
at Module._compile (module.js:569:30)
at Object.Module._extensions..js (module.js:580:10)
at Module.load (module.js:503:32)
at tryModuleLoad (module.js:466:12)
at Function.Module._load (module.js:458:3)
at Module.require (module.js:513:17)
at require (internal/module.js:11:18)
at Object. (/usr/local/lib/node_modules/write-good/write-good.js:4:18)
```

node v8.2.1

Start with the write-good CLI failure on Node v8.2.1 and inspect too-wordy/too-wordy.js at line 244, where the RegExp is constructed. Reproduce the reported error and check the generated expression's compatibility with that Node version. Done means the CLI can start without this invalid regular expression error.

Written by the indexing model from the issue text.