Lock resque scheduler on Ruby 1.9

Newer versions of resque-scheduler use the new hash syntax which means
they won't work with Ruby 1.9.3.

This commit locks resque-scheduler to an older version when we're using
less than Ruby 2.0.0

Fixes:

```
def evalsha(script, keys, argv, refresh: false)
                                        ^
/home/travis/build/rails/rails/vendor/bundle/ruby/1.9.1/gems/resque-scheduler-4.3.1/lib/resque/scheduler/lock/resilient.rb:78: syntax error, unexpected keyword_end, expecting $end
```

Gemfile

@@ -51,7 +51,7 @@ gem 'dalli', '>= 2.2.1'
 # ActiveJob
 group :job do
   gem 'resque', require: false
-  gem 'resque-scheduler', require: false
+  gem 'resque-scheduler', RUBY_VERSION < '2.0' ? '<= 4.3.0' : nil
   gem 'sidekiq', RUBY_VERSION < '2.2' ? '< 5' : nil, require: false
   gem 'sucker_punch', '< 2.0', require: false
   gem 'delayed_job', require: false

Gemfile.lock

@@ -284,7 +284,7 @@ DEPENDENCIES
   rake (>= 10.3)
   redcarpet (~> 3.1.2)
   resque
-  resque-scheduler
+  resque-scheduler (<= 4.3.0)
   ruby-prof (~> 0.11.2)
   sdoc (~> 0.4.0)
   sequel