Fixes an issue when running the "warmup".

[ivanmoore]

Without this fix, when I tried to run the "warmup" using:

docker run -p 80:3000 -e WARMUP=1 extreme_startup

When I go to http://127.0.0.1/controlpanel I see:

Internal server error

and there is a stack trace:

NoMethodError - undefined method round' for #<ExtremeStartup::WarmupQuestionFactory:0x00000000d9fb48>: /usr/src/app/lib/extreme_startup/web_server.rb:79:in block in class:WebServer'
/usr/local/bundle/gems/sinatra-1.2.6/lib/sinatra/base.rb:1152:in call' /usr/local/bundle/gems/sinatra-1.2.6/lib/sinatra/base.rb:1152:in block in compile!'
...

I don't know how to write a test for this, so here is the fix without an automated test.