gnu: ruby-2.2, ruby-2.1, ruby-1.8: Don't replace with ruby-2.3.3.

* gnu/packages/ruby.scm (ruby-2.2, ruby-2.1, ruby-1.8)[replacement]: New field.

gnu/packages/ruby.scm

@@ -123,6 +123,7 @@ (define ruby-2.3.3
 
 (define-public ruby-2.2
   (package (inherit ruby)
+    (replacement #f)
     (version "2.2.6")
     (source
      (origin
@@ -136,6 +137,7 @@ (define-public ruby-2.2
 
 (define-public ruby-2.1
   (package (inherit ruby)
+    (replacement #f)
     (version "2.1.10")
     (source
      (origin
@@ -169,6 +171,7 @@ (define-public ruby-2.1
 
 (define-public ruby-1.8
   (package (inherit ruby)
+    (replacement #f)
     (version "1.8.7-p374")
     (source
      (origin