title: YAML with erb is not parsing
body: <p>Why this yaml file won't parse?</p>
  
  <pre><code>---
  &lt;% sensor_types = YAML.load_file('db/seed-fixtures/sensor_type.yml') %&gt;
  &lt;% sensor_types.each do |sensor_type| %&gt;
  sensor&lt;%= sensor_type['id'] %&gt;:
    id: &lt;%= sensor_type['id'] %&gt;
    title: &lt;%= sensor_type['title'] %&gt;
    unit: "&lt;%= sensor_type['unit'] %&gt;"
    valid_min: &lt;%= sensor_type['valid_min'] %&gt;
    valid_max: &lt;%= sensor_type['valid_max'] %&gt;
    codename: &lt;%= sensor_type['codename'] %&gt;
    scale_base_ten_exponent: &lt;%= sensor_type['scale_base_ten_exponent'] %&gt;
  &lt;% end %&gt;
  </code></pre>
  
  <p>this file is used for fixtures in my tests, it is loaded by rspec from the fixtures directory.</p>
  
  <p>when I try it I get: "mapping values are not allowed in this context at line 4 column 28 (Psych::SyntaxError)"</p>