rubygems - Error while deploying rails app on heroku -

hi trying learn ruby on rail ruby.railstutorial.org , stuck @ point of deployment of app on heroku.when run

heroku run rake db:migrate 

i error:

running `rake db:migrate` attached terminal... up, run.3917 /usr/bin/env: ruby1.9.1: no such file or directory 

my ruby -v ruby 1.9.3p0 (2011-10-30 revision 33570) [x86_64-linux] , rails -v rails 4.0.0

here gemfile

source 'https://rubygems.org'   # bundle edge rails instead: gem 'rails', github: 'rails/rails' gem 'rails', '4.0.0'  # use sqlite3 database active record #gem 'sqlite3'  group :development   gem 'sqlite3', '1.3.7'   gem 'rspec-rails',      ">= 2.0.0.beta" end  group :doc   gem 'sdoc', '0.3.20', require: false end  # use scss stylesheets gem 'sass-rails', '~> 4.0.0'  # use uglifier compressor javascript assets gem 'uglifier', '>= 1.3.0'  # use coffeescript .js.coffee assets , views gem 'coffee-rails', '~> 4.0.0'  # see https://github.com/sstephenson/execjs#readme more supported runtimes # gem 'therubyracer', platforms: :ruby  # use jquery javascript library gem 'jquery-rails'  # turbolinks makes following links in web application faster.  gem 'turbolinks'  group :test   gem 'selenium-webdriver', '2.0.0'   gem 'capybara', '2.1.0' end  group :production   gem 'pg', '0.15.1'   gem 'rails_12factor', '0.0.2' end # build json apis ease. read more: https://github.com/rails/jbuilder gem 'jbuilder', '~> 1.2' 

why giving error ruby 1.9.1 when using 1.9.3 ?