Fix ArgumentError in Rails 3.2

[ryu39]

This PR fixes #115.

In Rails 3.2, ActiveRecord::FinderMethods#take does not exist ( added since Rails 4.0 http://apidock.com/rails/ActiveRecord/FinderMethods/take ), and ActiveRecord::Relation#take is processed as 'to_a.take' ( https://github.com/rails/rails/blob/3-2-stable/activerecord/lib/active_record/relation/delegation.rb#L40 ).
Array#take requires 1 argument ( https://ruby-doc.org/core-2.2.0/Array.html#method-i-take ), but no arguments are passed in SeedFu::Seeder#find_or_initialize_record, so ArgumentError is raised.

I have 3 ideas to fix this issue.

1. Revert take to first.
2. Use take(1).first instead of take.
3. Use limit(1).to_a.first instead of take.

I choose No. 3 because the SQL is same in Rails 3.2 and 4.0. And I also consider Pull #89.

User.where(name: 'Name').first
# Rails 3.2.22.5
#   => SELECT "users".* FROM "users" WHERE "users"."name" = 'Name' LIMIT 1
# Rails 4.0.13
#   => SELECT "users".* FROM "users" WHERE "users"."name" = 'Name' ORDER BY "users"."id" ASC LIMIT 1

User.where(name: 'Name').take(1).first
# Rails 3.2.22.5
#    => SELECT "users".* FROM "users" WHERE "users"."name" = 'Name'
# Rails 4.0.13
#    => SELECT "users".* FROM "users" WHERE "users"."name" = 'Name' LIMIT 1

User.where(name: 'Name').limit(1).to_a.first
# Rails 3.2.22.5
#    => SELECT "users".* FROM "users" WHERE "users"."name" = 'Name' LIMIT 1
# Rails 4.0.13
#    => SELECT "users".* FROM "users" WHERE "users"."name" = 'Name' LIMIT 1

If implicit order of ActiveRecord::FinderMethods#first (>= Rails 4.0) can be ignored, I think No. 1 may be better because it is easy to read.