fix invalid HTML center tag

Fixed the improper use of HTML center tag when building `authors.html`.

Changed `bin/gen-authors.sh` VERSION from to "1.4 2024-04-15"
to "1.5 2024-04-15".

Run `make gen_authors` to perform the above and test under macOS.

authors.html

@@ -123,8 +123,7 @@
 <!-- END: this line ends content from: inc/before-content.default.html -->
 <!-- START: this line starts content for HTML phase 21 by: bin/pandoc-wrapper.sh via bin/md2html.sh -->
 
-<center>
-<p>
+<p style="text-align:center;">
 Jump to authors starting with: [
 <a href="#A">A</a>  
 <a href="#B">B</a>  
@@ -153,7 +152,6 @@ Jump to authors starting with: [
 <a href="#Y">Y</a>  
 <a href="#Z">Z</a>]
 </p>
-</center>
 <p>
 <hr>
 <!-- A  A  A  A  A  A  A  A  A  A  A  A  A  A  A  A  A  A  A  A  A  A  A -->