[publications] update author list for WP manual

_fc-publications/wp/user-manual.md

 ---
 plugin: "wp"
-authors: "Patrick Baudin, François Bobot, Loïc Correnson, and Zaynah Dargaye"
+authors: "Patrick Baudin, François Bobot, Loïc Correnson, Zaynah Dargaye, Allan Blanchard"
 title: "WP Plug-in Manual"
 link: "http://frama-c.com/download/frama-c-wp-manual.pdf"
 category: manuals