[HTML] Use CDN for Whitney fonts

Related to #322

DiscordChatExporter.Domain/Exporting/Writers/Html/Core.css

@@ -2,31 +2,31 @@
 
 @font-face {
     font-family: Whitney;
-    src: url(https://discord.com/assets/6c6374bad0b0b6d204d8d6dc4a18d820.woff);
+    src: url(https://cdn.jsdelivr.net/gh/Tyrrrz/DiscordFonts@master/whitney-300.woff);
     font-weight: 300;
 }
 
 @font-face {
     font-family: Whitney;
-    src: url(https://discord.com/assets/e8acd7d9bf6207f99350ca9f9e23b168.woff);
+    src: url(https://cdn.jsdelivr.net/gh/Tyrrrz/DiscordFonts@master/whitney-400.woff);
     font-weight: 400;
 }
 
 @font-face {
     font-family: Whitney;
-    src: url(https://discord.com/assets/3bdef1251a424500c1b3a78dea9b7e57.woff);
+    src: url(https://cdn.jsdelivr.net/gh/Tyrrrz/DiscordFonts@master/whitney-500.woff);
     font-weight: 500;
 }
 
 @font-face {
     font-family: Whitney;
-    src: url(https://discord.com/assets/be0060dafb7a0e31d2a1ca17c0708636.woff);
+    src: url(https://cdn.jsdelivr.net/gh/Tyrrrz/DiscordFonts@master/whitney-600.woff);
     font-weight: 600;
 }
 
 @font-face {
     font-family: Whitney;
-    src: url(https://discord.com/assets/8e12fb4f14d9c4592eb8ec9f22337b04.woff);
+    src: url(https://cdn.jsdelivr.net/gh/Tyrrrz/DiscordFonts@master/whitney-700.woff);
     font-weight: 700;
 }