inline-style-prefixer should be a dependency, not devdependency

[jonathan-stone]

Getting "missing peer dependency" of inline-style-prefixer in npm install, and webpack build fails on an import of inline-style-prefixer.

Adding inline-style-prefixer as a dependency in my project's package.json fixes the issue, so I assume it should be a dependency in its own project.

Will create a PR if I get a chance.

[raffihsieh]

I've created a PR here: #6

[bentatum]

Thanks @raffihsieh