Fix UncaughtThrowError

UncaughtThrowError should subclass ArgumentError instead of
StandardError.

See https://github.com/ruby/ruby/blob/v2_2_0/NEWS#L72.

Author: tak1n

kernel/common/exception.rb

@@ -213,7 +213,7 @@ def to_s
   end
 end
 
-class UncaughtThrowError < StandardError
+class UncaughtThrowError < ArgumentError
 end
 
 class IndexError < StandardError