Use WOFF versions of SourceSansPro

See https://gitlab.com/gitlab-org/gitlab-ce/issues/6023

app/assets/fonts/OFL.txt

-Copyright 2010, 2012 Adobe Systems Incorporated (http://www.adobe.com/), with Reserved Font Name 'Source'. All Rights Reserved. Source is a trademark of Adobe Systems Incorporated in the United States and/or other countries.
+Copyright 2010, 2012, 2014 Adobe Systems Incorporated (http://www.adobe.com/), with Reserved Font Name 'Source'. All Rights Reserved. Source is a trademark of Adobe Systems Incorporated in the United States and/or other countries.
+
 This Font Software is licensed under the SIL Open Font License, Version 1.1.
-This license is copied below, and is also available with a FAQ at:
-http://scripts.sil.org/OFL
+
+This license is copied below, and is also available with a FAQ at: http://scripts.sil.org/OFL
 
 
 -----------------------------------------------------------

app/assets/stylesheets/framework/fonts.scss

@@ -3,23 +3,23 @@
   font-family: 'Source Sans Pro';
   font-style: normal;
   font-weight: 300;
-  src: local('Source Sans Pro Light'), local('SourceSansPro-Light'), font-url('SourceSansPro-Light.ttf');
+  src: local('Source Sans Pro Light'), local('SourceSansPro-Light'), font-url('SourceSansPro-Light.ttf.woff');
 }
 @font-face {
   font-family: 'Source Sans Pro';
   font-style: normal;
   font-weight: 400;
-  src: local('Source Sans Pro'), local('SourceSansPro-Regular'), font-url('SourceSansPro-Regular.ttf');
+  src: local('Source Sans Pro'), local('SourceSansPro-Regular'), font-url('SourceSansPro-Regular.ttf.woff');
 }
 @font-face {
   font-family: 'Source Sans Pro';
   font-style: normal;
   font-weight: 600;
-  src: local('Source Sans Pro Semibold'), local('SourceSansPro-Semibold'), font-url('SourceSansPro-Semibold.ttf');
+  src: local('Source Sans Pro Semibold'), local('SourceSansPro-Semibold'), font-url('SourceSansPro-Semibold.ttf.woff');
 }
 @font-face {
   font-family: 'Source Sans Pro';
   font-style: normal;
   font-weight: 700;
-  src: local('Source Sans Pro Bold'), local('SourceSansPro-Bold'), font-url('SourceSansPro-Bold.ttf');
+  src: local('Source Sans Pro Bold'), local('SourceSansPro-Bold'), font-url('SourceSansPro-Bold.ttf.woff');
 }