Ruby. Errors. DataMapper - ruby

Question

Try to use DataMapper on my macbook and got such error:
/Users/roger/.rvm/rubies/ruby-2.4.0/lib/ruby/site_ruby/2.4.0/rubygems
/specification.rb:2288:in `raise_if_conflicts':
Unable to activate dm-serializer-1.2.2, because json-2.1.0 conflicts
with json (~> 1.6) (Gem::ConflictError)
I try to uninstall JSON and install new. But if before ruby complain about JSON 1.6 now it complain about 2.10.
What to do I don't know..
Same script on my Ubuntu server work with DataMapper without problem but got Selenium error:
/usr/lib/ruby/2.3.0/net/protocol.rb:158:in `rbuf_fill': Net::ReadTimeout (Net::ReadTimeout)
from /usr/lib/ruby/2.3.0/net/protocol.rb:136:in `readuntil'
from /usr/lib/ruby/2.3.0/net/protocol.rb:146:in `readline'
from /usr/lib/ruby/2.3.0/net/http/response.rb:40:in `read_status_line'
from /usr/lib/ruby/2.3.0/net/http/response.rb:29:in `read_new'
from /usr/lib/ruby/2.3.0/net/http.rb:1437:in `block in transport_request'
from /usr/lib/ruby/2.3.0/net/http.rb:1434:in `catch'
from /usr/lib/ruby/2.3.0/net/http.rb:1434:in `transport_request'
from /usr/lib/ruby/2.3.0/net/http.rb:1407:in `request'
from /usr/lib/ruby/2.3.0/net/http.rb:1400:in `block in request'
from /usr/lib/ruby/2.3.0/net/http.rb:853:in `start'
from /usr/lib/ruby/2.3.0/net/http.rb:1398:in `request'
from /var/lib/gems/2.3.0/gems/selenium-webdriver-3.4.3/lib/selenium/webdriver/remote/http/default.rb:124:in `response_for'
from /var/lib/gems/2.3.0/gems/selenium-webdriver-3.4.3/lib/selenium/webdriver/remote/http/default.rb:78:in `request'
from /var/lib/gems/2.3.0/gems/selenium-webdriver-3.4.3/lib/selenium/webdriver/remote/http/common.rb:61:in `call'
from /var/lib/gems/2.3.0/gems/selenium-webdriver-3.4.3/lib/selenium/webdriver/remote/bridge.rb:170:in `execute'
from /var/lib/gems/2.3.0/gems/selenium-webdriver-3.4.3/lib/selenium/webdriver/remote/bridge.rb:103:in `create_session'
from /var/lib/gems/2.3.0/gems/selenium-webdriver-3.4.3/lib/selenium/webdriver/firefox/marionette/driver.rb:56:in `initialize'
from /var/lib/gems/2.3.0/gems/selenium-webdriver-3.4.3/lib/selenium/webdriver/firefox/driver.rb:33:in `new'
from /var/lib/gems/2.3.0/gems/selenium-webdriver-3.4.3/lib/selenium/webdriver/firefox/driver.rb:33:in `new'
from /var/lib/gems/2.3.0/gems/selenium-webdriver-3.4.3/lib/selenium/webdriver/common/driver.rb:54:in `for'
from /var/lib/gems/2.3.0/gems/selenium-webdriver-3.4.3/lib/selenium/webdriver.rb:86:in `for'
from selen_serv.rb:19:in `<main>'
Script header:
require 'nokogiri'
require 'selenium-webdriver'
require 'rspec/expectations'
require 'headless'
require 'pp'
require 'json'
require 'rubygems'
require 'data_mapper'
require 'dm-core'
require 'dm-validations'
require 'dm-timestamps'
TEST_DIR = File.expand_path(File.dirname(__FILE__))
TEST_FILES = File.join(TEST_DIR, "test_files")
TEST_OUTPUT = File.join(TEST_DIR, "test_output")
CHROMEDRIVER_FN = File.join(File.absolute_path('..', TEST_DIR), "/usr/local/bin", "chromedriver")
#browser = Selenium::WebDriver.for :firefox
bash-3.2$ bundler
Resolving dependencies...
Bundler could not find compatible versions for gem "json_pure":
In Gemfile:
data_mapper was resolved to 1.2.0, which depends on
dm-serializer (~> 1.2.0) was resolved to 1.2.2, which depends on
json_pure (~> 1.6)
Could not find gem 'json_pure (~> 1.6)', which is required by gem 'dm-serializer (~> 1.2.0)', in any of the sources.