Minor documentation tweak

I got a little tripped up here since I copied and pasted this snippet as a place to start. The error message that rails gives `ArgumentError in JasmineRails::SpecRunner#index` with details of `Showing /path/to/gems/jasmine-rails/app/views/layouts/jasmine_rails/spec_runner.html.erb where line #8 raised:` is slightly misleading (though it does point you to the correct file when describing the error later (`wrong number of arguments (3 for 1) (in /path/to/myapp/spec/javascripts/welcome_spec.js:2)`).

Making this change doesn't really seem to hurt anything and make keep others from making the same mistake.