Tell to run bundle in the Heroku deploy instructions

Without running first `bundle` I get the following error when running `heroku config:add SECRET_TOKEN="$(bundle exec rake secret)"`

/Users/florent2/.rbenv/versions/2.0.0-p0/lib/ruby/gems/2.0.0/gems/bundler-1.3.5/lib/bundler/spec_set.rb:92:in `block in materialize': Could not find i18n-0.6.1 in any of the sources (Bundler::GemNotFound)
Merge pull request #513 from Florent2/patch-1

Tell to run `bundle` in the Heroku deploy instructions
Treat message as CDATA to avoid invalid XML
Properly escape backtrace attributes to avoid invalid XML
Merge pull request #514 from mildavw/master

fix for notifier.js sending invalid XML
Merge pull request #517 from roryf/master

Fixes notifier.js sending invalid XML in backtrace lines
update changelog with new Pull request merge [ci-skip]
Pass problem when you UpdateProblemCache by rake task

Fix #518
update changelog with issue fix [ci-skip]
Sign in input set type=email for mobile browsers keyboard
Email only unless user_has_username
Merge pull request #519 from nyaa/email_input

Sign in: email input type=email for mobile browsers keyboard
Configure for LDAP authentication
Ignore LDAP config
Correct detection/storage of name and email
Fix creating users on first login
Work around libv8 build issues on 64 bit

See https://github.com/cowboyd/therubyracer/issues/215
Switch back to LDAP auth