Fix image path

books/naheulbeuk.sb

@@ -8,7 +8,7 @@
   ],
 "booktype" : "chorded",
 "footer" : "Musique du Naheulband: \\url{http://www.penofchaos.com/warham/donjon-groupe.htm}",
-"picture" : "nb_cover",
+"picture" : "img/nb_cover",
 "picturecopyright" : "Personnages par \\emph{Pen Of Chaos} / Illustrations par \\emph{Marion Poinsot}",
 "subtitle" : "Recueil de chansons non-officiel",
 "title" : "Le Donjon de Naheulbeuk",

books/volume-1.sb

@@ -7,7 +7,7 @@
     "pictures"
   ],
 "booktype" : "chorded",
-"picture" : "feel-the-music",
+"picture" : "img/feel-the-music",
 "picturecopyright" : "foxygamergirl @ deviantart.com",
 "subtitle" : "Tome 1",
 "content" : [["sorted",

books/volume-2.sb

@@ -7,7 +7,7 @@
     "pictures"
   ],
 "booktype" : "chorded",
-"picture" : "sound",
+"picture" : "img/sound",
 "picturecopyright" : "ellesh @ deviantart.com",
 "subtitle" : "Tome 2",
 "content" : [["sorted",

books/volume-3.sb

@@ -7,7 +7,7 @@
     "pictures"
   ],
 "booktype" : "chorded",
-"picture" : "Mousey_Band_by_Duffzilla",
+"picture" : "img/Mousey_Band_by_Duffzilla",
 "picturecopyright" : "duffzilla @ deviantart.com",
 "subtitle" : "Tome 3",
 "content" : [["sorted",

books/volume-4.sb

@@ -7,7 +7,7 @@
     "pictures"
   ],
 "booktype" : "chorded",
-"picture" : "music_by_lauratheartist",
+"picture" : "img/music_by_lauratheartist",
 "picturecopyright" : "LauraTheArtist @ deviantart.com",
 "subtitle" : "Tome 4",
 "content" : [["sorted",

books/volume-5.sb

@@ -7,7 +7,7 @@
     "pictures"
   ],
 "booktype" : "chorded",
-"picture" : "The_Music_Machine_by_hit_squad",
+"picture" : "img/The_Music_Machine_by_hit_squad",
 "picturecopyright" : "hit-squad @ deviantart.com",
 "subtitle" : "Tome 5",
 "content" : [["sorted",