Change names in URL schema to singular form.

templates/base.html

@@ -13,10 +13,10 @@
 
 {% block navbar %}
 {%  set nav_bar = [
-    ('/seasons', 'seasons', 'Seasons', 'fas fa-calendar'),
-    ('/players', 'players', 'Players', 'fas fa-users'),
-    ('/enemies', 'enemies', 'Enemies', 'fas fa-skull-crossbones'),
-    ('/drinks', 'drinks', 'Drinks', 'fas fa-beer')
+    ('/season', 'seasons', 'Seasons', 'fas fa-calendar'),
+    ('/player', 'players', 'Players', 'fas fa-users'),
+    ('/enemie', 'enemies', 'Enemies', 'fas fa-skull-crossbones'),
+    ('/drink', 'drinks', 'Drinks', 'fas fa-beer')
   ]-%}
   <div class="container">
     <nav class="navbar navbar-expand-lg bg-dark navbar-dark">