Fix 'use_threshold' usage inside of DNSXLCheck

lib/dnsxl_check.rb

@@ -26,8 +26,12 @@ class DNSXLCheck
     dnsxl_check
   end
+  def initialize
+    @use_threshold = true
+  end
+
   def test(ip)
-    if use_threshold?
+    if @use_threshold
       test_with_threshold(ip)
     else
       test_strict(ip)
@@ -52,10 +56,6 @@ class DNSXLCheck
     @use_threshold = value == true
   end
-  def use_threshold?
-    @use_threshold &&= true
-  end
-
   def threshold=(threshold)
     raise ArgumentError, "'threshold' value must be grather than 0 and less than or equal to 1" unless threshold > 0 && threshold <= 1
     @threshold = threshold