Fixed mashape api key loading

src/NadekoBot/Services/IBotCredentials.cs

@@ -10,7 +10,7 @@ namespace NadekoBot.Services
         string Token { get; }
         string GoogleApiKey { get; }
         ulong[] OwnerIds { get; }
-        IEnumerable<string> MashapeKey { get; }
+        string MashapeKey { get; }
         string LoLApiKey { get; }
 
         bool IsOwner(IUser u);

src/NadekoBot/Services/Impl/BotCredentials.cs

@@ -17,7 +17,7 @@ namespace NadekoBot.Services.Impl
 
         public string GoogleApiKey { get; }
 
-        public IEnumerable<string> MashapeKey { get; }
+        public string MashapeKey { get; }
 
         public string Token { get; }
 
@@ -46,7 +46,7 @@ namespace NadekoBot.Services.Impl
             public ulong[] OwnerIds { get; set; }
             public string LoLApiKey { get; set; }
             public string GoogleApiKey { get; set; }
-            public IEnumerable<string> MashapeKey { get; set; }
+            public string MashapeKey { get; set; }
         }
 
         public bool IsOwner(IUser u) => OwnerIds.Contains(u.Id);