Version bump to 1.0.0

This pull request bumps the version to 1.0.0. 

The version_info was already bumped in https://github.com/sprockets/sprockets.mixins.json_error/commit/ca9e0b535b0b79b497cc8db17bcfccaec29d9da4#diff-b02c64f3815092b41cbf0931ab5d8917R7