News: Use KSP_URL as a constant

And don't have it copied everywhere

hrochobot/cogs/news.py

@@ -6,7 +6,7 @@ from markdownify import markdownify
 import re
 from bs4 import BeautifulSoup
 
-from hrochobot.utils.ksp_utils import ksp_feed
+from hrochobot.utils.ksp_utils import ksp_feed, KSP_URL
 import hrochobot.utils.data as data
 
 NEWS_JSON = "news"
@@ -43,7 +43,7 @@ def format_entry(entry, author=None):
     if author:
         embed.set_author(name=author)
 
-    embed.set_thumbnail(url="https://ksp.mff.cuni.cz/img/hippo_head.png")
+    embed.set_thumbnail(url=f"{KSP_URL}/img/hippo_head.png")
 
     date = datetime.fromisoformat(entry.published)
     embed.set_footer(text=date.strftime("%-d. %-m. %Y"))
@@ -57,7 +57,7 @@ async def post_news(bot, guild, entry_id):
 
     channel = get(guild.channels, id=news_json["news_channel"])
     feed = await ksp_feed()
-    entries_with_id = list(filter(lambda e: e.id == f"https://ksp.mff.cuni.cz/{entry_id}", feed.entries))
+    entries_with_id = list(filter(lambda e: e.id == f"{KSP_URL}/{entry_id}", feed.entries))
     if len(entries_with_id) == 0:
         return f"Entry with id ``{entry_id}`` not found."