gecko-search-button gets current Boost version (boostorg#1903)

Author: ashtum

templates/includes/_legacy_docs_header.html

@@ -19,7 +19,7 @@ <h1 class="heading-title">
     Alexandrescu</a>, <a href="https://books.google.com/books/about/C++_Coding_Standards.html?id=mmjVIC6WolgC" class="external">C++
     Coding Standards</a></span></p>
     <div class="heading-search">
-      <button id="gecko-search-button" data-current-boost-version="1.88.0" data-theme-mode="light" data-font-family="sans-serif">
+      <button id="gecko-search-button" data-current-boost-version="{{ current_version.stripped_boost_url_slug }}" data-theme-mode="light" data-font-family="sans-serif">
         <svg viewBox="0 0 24 24">
           <path d="M15.5 14h-.79l-.28-.27C15.41 12.59 16 11.11 16 9.5 16 5.91 13.09 3 9.5 3S3 5.91 3 9.5 5.91 16 9.5 16c1.61 0 3.09-.59 4.23-1.57l.27.28v.79l5 4.99L20.49 19l-4.99-5zm-6 0C7.01 14 5 11.99 5 9.5S7.01 5 9.5 5 14 7.01 14 9.5 11.99 14 9.5 14z"></path>
         </svg>Search...