[DOC] Use Integer instead of Fixnum [ci skip]

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@57431 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

lib/weakref.rb

@@ -78,7 +78,7 @@ class WeakRef < Delegator
   # Creates a weak reference to +orig+
   #
   # Raises an ArgumentError if the given +orig+ is immutable, such as Symbol,
-  # Fixnum, or Float.
+  # Integer, or Float.
 
   def initialize(orig)
     case orig