Source Serif Pro regular and bold 2.007, and italic 1.007

Use fonts from the Roman 2.007 and Italic 1.007 version at:
https://github.com/adobe-fonts/source-serif-pro/releases/tag/2.007R-ro%2F1.007R-it

The following files are used from the distribution:

  * WOFF/TTF/SourceSerifPro-Regular.ttf.woff
  * WOFF/TTF/SourceSerifPro-Bold.ttf.woff
  * WOFF/TTF/SourceSerifPro-It.ttf.woff

These replace the older Source Serif Pro regular and bold fonts, and
the Heuristica italic font.

Author: tspiteri

src/librustdoc/html/static/COPYRIGHT.txt

@@ -12,21 +12,6 @@ included, and carry their own copyright notices and license terms:
     Licensed under the SIL Open Font License, Version 1.1.
     See FiraSans-LICENSE.txt.
 
-* Heuristica (Heuristica-Italic.woff):
-
-    Copyright 1989, 1991 Adobe Systems Incorporated. All rights reserved.
-    Utopia is either a registered trademark or trademark of Adobe Systems
-    Incorporated in the United States and/or other countries. Used under
-    license.
-
-    Copyright 2006 Han The Thanh, Vntopia font family, http://vntex.sf.net
-
-    Copyright (c) 2008-2012, Andrey V. Panov ([email protected]),
-    with Reserved Font Name Heuristica.
-
-    Licensed under the SIL Open Font License, Version 1.1.
-    See Heuristica-LICENSE.txt.
-
 * rustdoc.css, main.js, and playpen.js:
 
     Copyright 2015 The Rust Developers.
@@ -47,7 +32,8 @@ included, and carry their own copyright notices and license terms:
     Licensed under the SIL Open Font License, Version 1.1.
     See SourceCodePro-LICENSE.txt.
 
-* Source Serif Pro (SourceSerifPro-Regular.woff, SourceSerifPro-Bold.woff):
+* Source Serif Pro (SourceSerifPro-Regular.ttf.woff,
+    SourceSerifPro-Bold.ttf.woff, SourceSerifPro-It.ttf.woff):
 
     Copyright 2014 Adobe Systems Incorporated (http://www.adobe.com/), with
     Reserved Font Name 'Source'. All Rights Reserved. Source is a trademark of