Require 'cells' as a dependency
Require 'cells' as a dependency

Currently, the 'cells' gem is a dependency, but is not explicitly required.
Implicitly relying on 'cells' to be required by the consuming application causes
an 'uninitialized constant' error when requiring this gem in isolation.

This closes apotonick/cells#374.

trailblazer/cells-erb,trailblazer/cells-erb