Use Time::Span.zero instead of constructor with 0 nanoseconds

src/spectator/pending_result.cr

@@ -19,7 +19,7 @@ module Spectator
     end
 
     def initialize(@example)
-      super(@example, Time::Span.new(nanoseconds: 0))
+      super(@example, Time::Span.zero)
     end
   end
 end

src/spectator/runnable_example.cr

@@ -47,7 +47,7 @@ module Spectator
     protected abstract def run_instance
 
     private class ResultCapture
-      property elapsed = Time::Span.new(nanoseconds: 0)
+      property elapsed = Time::Span.zero
       property error : Exception?
     end
   end