0.15.2 documentation: link to 0.15.2 std docs

Fixes #554

Author: squeek502

src/documentation/0.15.2/index.html

@@ -788,7 +788,7 @@ <h2 id="Introduction"><a href="#toc-Introduction">Introduction</a> <a class="hdr
       <h2 id="Zig-Standard-Library"><a href="#toc-Zig-Standard-Library">Zig Standard Library</a> <a class="hdr" href="#Zig-Standard-Library">§</a></h2>
 
       <p>
-        The <a href="https://ziglang.org/documentation/master/std/">Zig Standard Library</a> has its own documentation.
+        The <a href="https://ziglang.org/documentation/0.15.2/std/">Zig Standard Library</a> has its own documentation.
       </p>
       <p>
         Zig's Standard Library contains commonly used algorithms, data structures, and definitions to help you build programs or libraries.