Updated dev dependencies to latest versions.
These files are copied to vendor by grunt and should not be in git.
Merge pull request #337 from alphagov/feature/dev-dependencies

Updated dev dependencies to latest versions.
Merge pull request #339 from alphagov/feature/ignore-files

These files are copied to vendor by grunt and should not be in git.
Updated packages to latest versions
lodash should be copied to vendor as part of the grunt task.
This shouldn't be in version control