Fix undefined method .path on nil

Hi,

I got a undefined method call on .nil at line 106 of spring/application.rb.
After deeper investigation I've found out that my Gemfile didn't have sinatra, but other gem required it.
That caused spring to fail loading of rails app and crash.

This simple change checks that Rails.application is there before accessing it.

With this change it raises proper message that required file is not there.
replace and by &&
Merge pull request #246 from mikz/patch-1

Fix undefined method .path on nil
Test helper fix
Recommend 1.1 upgraders to regenerate binstubs
Add contributing guide [ci skip]

Closes #251.
Fix setting of process title causing rspec breakage

Fixes https://github.com/jonleighton/spring-commands-rspec/issues/7
Connect a PTY when preloading in background

Readline + libedit gets messed up if it loads when not connected to a
terminal. This resolves that problem.

Fixes #244.
Bump to version 1.1.1