langref: Bump 0.15.1 to 0.15.2

Author: squeek502

doc/langref.html.in

@@ -317,7 +317,7 @@
           <a href="https://ziglang.org/documentation/0.12.0/">0.12.0</a> |
           <a href="https://ziglang.org/documentation/0.13.0/">0.13.0</a> |
           <a href="https://ziglang.org/documentation/0.14.1/">0.14.1</a> |
-          <a href="https://ziglang.org/documentation/0.15.1/">0.15.1</a> |
+          <a href="https://ziglang.org/documentation/0.15.2/">0.15.2</a> |
           master
         </nav>
         <nav aria-labelledby="table-of-contents">