Ensure specified environment is used

If for any reason RAILS_ENV was set to test this command will start a
Rails server with test environment:

    rails s -e development

But this one will start with development environment:

    RAILS_ENV=development rails s

I am not sure who is at fault here, but this ensures guard-rails will
always use the environment specified by the environment option.
Merge pull request #18 from mmacedo/environment

Ensure specified environment is used
bump version
send kill after send sigint to ensure rails is down
add pid_file option
support zeus to boost rails init
refactory build_rails_command
specify mocha version to ensure test not broken
fix pid_file cannot monitored issue
update old info in README
update gemspec
use mocha_standalone to avoid warning
update readme
ensure kill server
cleanup useless spaces in spec
improve zeus options
add pid_file rspec test
bump to 0.2.0
update readme and add badges
fix dependencies version