Fix two damaged figure tags

Author: marijnh

17_canvas.md

@@ -590,7 +590,9 @@ a single image file and then draw only the part you need. For example,
 we have this picture containing a game character in multiple
 ((pose))s:
 
-{{figure {url: "img/player_big.png", alt: "Various poses of a game character",width: "6cm", [animation, "platform game"]}}}
+{{figure {url: "img/player_big.png", alt: "Various poses of a game character",width: "6cm"}}}
+
+{{index [animation, "platform game"]}}
 
 By alternating which pose we draw, we can show an animation that
 looks like a walking character.

18_http.md

@@ -13,7 +13,9 @@ quote}}
 
 {{index "Fielding, Roy"}}
 
-{{figure {url: "img/chapter_picture_18.jpg", alt: "Picture of a web form on a medieval scroll", chapter: "framed", [browser, environment]}}}
+{{figure {url: "img/chapter_picture_18.jpg", alt: "Picture of a web form on a medieval scroll", chapter: "framed"}}}
+
+{{index [browser, environment]}}
 
 The _Hypertext Transfer Protocol_, already mentioned in [Chapter
 ?](browser#web), is the mechanism through which data is requested and