title: Postcss-cli cannot find flexbugs-fixes module (finds autoprefixer with no problems though)
body: <p>I installed postcss-cli autoprefixer and postcss-flexbugs-fixes in my project via npm.  There were unmet dep warnings for pff but it did install.  I know my postcss and cli is working because when I run</p>
  
  <pre><code>postcss --use autoprefixer index.scss
  </code></pre>
  
  <p>from terminal it works just fine - i have some dummy css in there anyway just to rule out syntax errors.</p>
  
  <p>When I run </p>
  
  <pre><code>postcss --use postcss-flexbugs-fixes index.scss
  </code></pre>
  
  <p>I get an error saying cannot find module postcss-flexbugs-fixes.  It's probably worth mentioning I'm on node 4.4.5 but I've had postcss-flexbugs-fixes work before on this version of node, the only difference (including version numbers) being it was wrapped inside a gulp task.
  Here is the full error:</p>
  
  <pre><code>Error: Cannot find module 'postcss-flexbugs-fixes'
  at Function.Module._resolveFilename (module.js:325:15)
  at Function.Module._load (module.js:276:25)
  at Module.require (module.js:353:17)
  at require (internal/module.js:12:17)
  at /Users/ohu275/.nvm/versions/node/v4.4.5/lib/node_modules/postcss-cli/index.js:107:14
  at Array.map (native)
  at Object.&lt;anonymous&gt; (/Users/ohu275/.nvm/versions/node/v4.4.5/lib/node_modules/postcss-cli/index.js:100:24)
  at Module._compile (module.js:409:26)
  at Object.Module._extensions..js (module.js:416:10)
  at Module.load (module.js:343:32)
  </code></pre>
  
  <p>I'm ultimately trying to get to a point where I can run my postcss tasks via an npm build script.  I've got autoprefixer working but no dice with the flexbugs-fixes via postcss-cli.  I have to think I'm doing something wrong because I've had this particular plugin work before, just not with the cli.  Other plugins are working with my cli.  Any help would be much appreciated.</p>