My Rails s命令无效，下面是我得到的。第7行，语法错误是：需要'psych / parser'。不确定如何纠正此错误。
/home/vagrant/.rvm/rubies/ruby-2.0.0-p481/lib/ruby/2.0.0/psych.rb:205:in `parse': (<unknown>): found character that cannot start any token while scanning for the next token at line 7 column 1 (Psych::SyntaxError)
from /home/vagrant/.rvm/rubies/ruby-2.0.0-p481/lib/ruby/2.0.0/psych.rb:205:in `parse_stream'
from /home/vagrant/.rvm/rubies/ruby-2.0.0-p481/lib/ruby/2.0.0/psych.rb:153:in `parse'
from /home/vagrant/.rvm/rubies/ruby-2.0.0-p481/lib/ruby/2.0.0/psych.rb:129:in `load'
from /home/vagrant/.rvm/gems/ruby-2.0.0-p481/gems/figaro-0.7.0/lib/figaro.rb:21:in `raw'
from /home/vagrant/.rvm/gems/ruby-2.0.0-p481/gems/figaro-0.7.0/lib/figaro.rb:17:in `env'
from /home/vagrant/.rvm/gems/ruby-2.0.0-p481/gems/figaro-0.7.0/lib/figaro/railtie.rb:7:in `block in <class:Railtie>'
from /home/vagrant/.rvm/gems/ruby-2.0.0-p481/gems/activesupport-4.1.5/lib/active_support/lazy_load_hooks.rb:36:in `call'
from /home/vagrant/.rvm/gems/ruby-2.0.0-p481/gems/activesupport-4.1.5/lib/active_support/lazy_load_hooks.rb:36:in `execute_hook'
from /home/vagrant/.rvm/gems/ruby-2.0.0-p481/gems/activesupport-4.1.5/lib/active_support/lazy_load_hooks.rb:45:in `block in run_load_hooks'
from /home/vagrant/.rvm/gems/ruby-2.0.0-p481/gems/activesupport-4.1.5/lib/active_support/lazy_load_hooks.rb:44:in `each'
from /home/vagrant/.rvm/gems/ruby-2.0.0-p481/gems/activesupport-4.1.5/lib/active_support/lazy_load_hooks.rb:44:in `run_load_hooks'
from /home/vagrant/.rvm/gems/ruby-2.0.0-p481/gems/railties-4.1.5/lib/rails/application.rb:123:in `initialize'
from /home/vagrant/.rvm/gems/ruby-2.0.0-p481/gems/railties-4.1.5/lib/rails/railtie.rb:171:in `new'
from /home/vagrant/.rvm/gems/ruby-2.0.0-p481/gems/railties-4.1.5/lib/rails/railtie.rb:171:in `instance'
from /home/vagrant/.rvm/gems/ruby-2.0.0-p481/gems/railties-4.1.5/lib/rails/application.rb:90:in `inherited'
from /home/vagrant/code/bloccit/config/application.rb:17:in `<module:Bloccit>'
from /home/vagrant/code/bloccit/config/application.rb:16:in `<top (required)>'
from /home/vagrant/.rvm/gems/ruby-2.0.0-p481/gems/railties-4.1.5/lib/rails/commands/commands_tasks.rb:79:in `require'
from /home/vagrant/.rvm/gems/ruby-2.0.0-p481/gems/railties-4.1.5/lib/rails/commands/commands_tasks.rb:79:in `block in server'
from /home/vagrant/.rvm/gems/ruby-2.0.0-p481/gems/railties-4.1.5/lib/rails/commands/commands_tasks.rb:76:in `tap'
from /home/vagrant/.rvm/gems/ruby-2.0.0-p481/gems/railties-4.1.5/lib/rails/commands/commands_tasks.rb:76:in `server'
from /home/vagrant/.rvm/gems/ruby-2.0.0-p481/gems/railties-4.1.5/lib/rails/commands/commands_tasks.rb:40:in `run_command!'
from /home/vagrant/.rvm/gems/ruby-2.0.0-p481/gems/railties-4.1.5/lib/rails/commands.rb:17:in `<top (required)>'
from /home/vagrant/code/bloccit/bin/rails:8:in `require'
from /home/vagrant/code/bloccit/bin/rails:8:in `<top (required)>'
from /home/vagrant/.rvm/gems/ruby-2.0.0-p481/gems/spring-1.1.3/lib/spring/client/rails.rb:27:in `load'
from /home/vagrant/.rvm/gems/ruby-2.0.0-p481/gems/spring-1.1.3/lib/spring/client/rails.rb:27:in `call'
from /home/vagrant/.rvm/gems/ruby-2.0.0-p481/gems/spring-1.1.3/lib/spring/client/command.rb:7:in `call'
from /home/vagrant/.rvm/gems/ruby-2.0.0-p481/gems/spring-1.1.3/lib/spring/client.rb:26:in `run'
from /home/vagrant/.rvm/gems/ruby-2.0.0-p481/gems/spring-1.1.3/bin/spring:48:in `<top (required)>'
from /home/vagrant/.rvm/gems/ruby-2.0.0-p481/gems/spring-1.1.3/lib/spring/binstub.rb:11:in `load'
from /home/vagrant/.rvm/gems/ruby-2.0.0-p481/gems/spring-1.1.3/lib/spring/binstub.rb:11:in `<top (required)>'
from /home/vagrant/code/bloccit/bin/spring:16:in `require'
from /home/vagrant/code/bloccit/bin/spring:16:in `<top (required)>'
from bin/rails:3:in `load'
from bin/rails:3:in `<main>'