title: How to install libicu-dev on Ubuntu
body: <p>I am trying install gollum by gem on Ubuntu 14.10.</p>
  
  <p>When I try to use <code>gem install gollum</code>, I see the error below:</p>
  
  <pre><code>/usr/bin/ruby2.1 extconf.rb
  mkmf.rb can't find header files for ruby at /usr/lib/ruby/include/ruby.h
  ERROR:  Error installing gollum:
      ERROR: Failed to build gem native extension.
  
      Building has failed. See above output for more information on the failure.
  extconf failed, exit code 1
  
  Gem files will remain installed in /var/lib/gems/2.1.0/gems/charlock_holmes-0.7.3 for inspection.
  Results logged to /var/lib/gems/2.1.0/extensions/x86_64-linux/2.1.0/charlock_holmes-0.7.3/gem_make.out
  </code></pre>
  
  <p>I found out that <code>libicu-dev</code> is required.</p>
  
  <p>So I use <code>sudo apt-get install libicu-dev</code>, but receive this error:</p>
  
  <pre><code>$ sudo apt-get install libicu-dev 
  Reading package lists... Done
  Building dependency tree       
  Reading state information... Done
  Some packages could not be installed. This may mean that you have
  requested an impossible situation or if you are using the unstable
  distribution that some required packages have not yet been created
  or been moved out of Incoming.
  The following information may help to resolve the situation:
  
  The following packages have unmet dependencies:
   libicu-dev : Depends: libicu52 (= 52.1-6) but 52.1-6ubuntu0.3 is to be installed
  E: Unable to correct problems, you have held broken packages.
  </code></pre>
  
  <p>I tried <code>apt-get install -f</code>, but the error remained as before.</p>
  
  <p>How can I fix the problem? Thank you!</p>