Fix call to NSLog when logging

Calling `NSLog(message!)` will interpret message as format string (see
[docs](https://developer.apple.com/documentation/foundation/1395275-nslog),
causing errors and even segfault in some edge cases. Instead, use proper
format string  and message as argument.

Fixes johnste#328.

Finicky/Finicky/API.swift

@@ -20,7 +20,7 @@ import JavaScriptCore
 
     static func log(_ message: String?) {
         if message != nil {
-            NSLog(message!)
+            NSLog("%@", message!)
             logToConsole?(message!, false)
         }
     }