安装popHealth project的演示服务器。运行以下安装命令时出现以下错误：
bundle exec rake bundle:import[/home/pophealth/bundle-2.6.0.zip,false,false,'*',true,true] RAILS_ENV=development
WARNING: Nokogiri was built against LibXML version 2.8.0, but has dynamically loaded 2.7.8
/home/<removed>/popHealth/lib/tasks/sharding.rake:4: warning: class variable access from toplevel
rake aborted!
Errno::ENOENT: No such file or directory @ rb_sysopen - /home/pophealth/bundle-2.6.0.zip
/usr/local/rvm/gems/ruby-2.1.2/gems/health-data-standards-3.5.3/lib/health-data-standards/tasks/bundle.rake:41:in `initialize'
/usr/local/rvm/gems/ruby-2.1.2/gems/health-data-standards-3.5.3/lib/health-data-standards/tasks/bundle.rake:41:in `open'
/usr/local/rvm/gems/ruby-2.1.2/gems/health-data-standards-3.5.3/lib/health-data-standards/tasks/bundle.rake:41:in `block (2 levels) in <top (required)>'
/usr/local/rvm/gems/ruby-2.1.2/bin/ruby_executable_hooks:15:in `eval'
/usr/local/rvm/gems/ruby-2.1.2/bin/ruby_executable_hooks:15:in `<main>'
Tasks: TOP => bundle:import
(See full trace by running task with --trace)
所以看来我需要更高版本的LibXML，对吧？研究，研究...... 发出以下命令：
sudo apt-get install --only-upgrade libxml2 libxml2-dev
Reading package lists... Done
Building dependency tree
Reading state information... Done
libxml2 is already the newest version.
libxml2-dev is already the newest version.
0 upgraded, 0 newly installed, 0 to remove and 0 not upgraded.
所以我不知所措。显然有一个更高版本的libxml2，但我无法升级它。我猜我需要配置我的系统在其他地方搜索它，但我不知道如何做到这一点。假设这是正确的，我遇到的重大问题是：
1）如何找到包含我需要安装的libxml2版本的repo。
2）一旦找到该回购，我该如何配置apt-get来代替使用该回购。