Splat the arguments to strong_parameters#permit, fixes #2716

There is a discrepancy between rails' strong_parameter implementation,
and the strong_parameter gem's[0]. While this is obviously a problem
with the other gem, it doesn't hurt to explicitly splat the parameters.

[0]: https://github.com/rails/strong_parameters/pull/170
Merge pull request #2717 from memberful/2716-splat-sanitize-params

Splat the arguments to strong_parameters#permit, fixes #2716