Fixes rust-lang/book#29 where the navigation arrow for next chapter was displayed on top of the scroll bar making it unusable

Author: azerupi

src/theme/book.css

@@ -222,7 +222,7 @@ h3 {
   left: 0;
 }
 .next {
-  right: 0;
+  right: 15px;
 }
 .theme-popup {
   position: fixed;

src/theme/stylus/nav-icons.styl

@@ -20,4 +20,4 @@
 .mobile-nav-chapters { display: none }
 .nav-chapters:hover { text-decoration: none }
 .previous { left: 0 }
-.next { right: 0 }
+.next { right: 15px }