Get correct placement of header files

-Hd didn't work, header files were simply dumped in the root dir.

build.d

@@ -154,7 +154,7 @@ void buildHeaders()
         ensureDir(d);
 
         immutable diName = baseName(s, ".d")~".di";
-        immutable cmd = "dmd "~s~" -c -o- -H -Hd"~d~" -Hf"~diName;
+        immutable cmd = "dmd "~s~" -c -o- -H -Hf"~d~diName;
         writeln(cmd);
         enforce(system(cmd) == 0, "Error making header file: "~diName);
     }