(maint) Standardize on /usr/bin/env ruby -S rspec
Without this patch some spec files are using ruby -S rspec and others
are using rspec.
We should standardize on a single form of the interpreter used for spec
files.
ruby -S rspec is the best choice because it correctly informs editors
such as Vim with Syntastic that the file is a Ruby file rather than an
Rspec file.