refactor call to find(:first) to quiet deprecation warnings

DEPRECATION WARNING: Calling #find(:first) is deprecated. Please call #first directly instead. (called from edit at ~/surveyor/lib/surveyor/surveyor_controller_methods.rb:63)

Refactored so that we call either first() or find() depending on
whether we've got a primary key or not.

lib/surveyor/surveyor_controller_methods.rb

@@ -60,7 +60,7 @@ def edit
       if @response_set
         @survey = Survey.with_sections.find_by_id(@response_set.survey_id)
         @sections = @survey.sections
-        @section = @sections.with_includes.find(section_id_from(params) || :first) || @sections.with_includes.first
+        @section = section_id_from(params) ? @sections.with_includes.find(section_id_from(params)) : @sections.with_includes.first
         set_dependents
       else
         flash[:notice] = t('surveyor.unable_to_find_your_responses')