Apply noindesx at docs page with version =! 9

Author: ujibang

_includes/head.html

@@ -11,7 +11,7 @@
    <meta property="og:title" content="{% if page.title %}RESTHeart - {{ page.title }}{% else %}{{ site.title }}{% endif %}">
    <meta property="og:description" content="{% if page.excerpt %}{{ page.excerpt | strip_html | strip_newlines | truncate: 160 }}{% else %}{{ site.description }}{% endif %}">
    <meta property="og:locale" content="en">
-   {% if page.docs_version != null and page.docs_version != 8 %}
+   {% if page.docs_version != null and page.docs_version != 9 %}
    <!-- avoid search engine indexing of old documentation pages  -->
    <meta name="robots" content="noindex,nofollow">
    {% endif %}