Update Gemfile & Gemspec

Signed-off-by: Aymeric Brisse <aymeric.brisse@perfect-memory.com>
Update Rakefile

Signed-off-by: Aymeric Brisse <aymeric.brisse@perfect-memory.com>
Update .gitignore

Signed-off-by: Aymeric Brisse <aymeric.brisse@perfect-memory.com>