spec: s/and/or/ for correctness and parallelism

No change to the meaning, just bad writing found by
Doug McIlroy.
Let's start the new year off with a bang.

R=golang-codereviews, bradfitz, dave
CC=golang-codereviews
https://golang.org/cl/47110044

doc/go_spec.html

 <!--{
 	"Title": "The Go Programming Language Specification",
-	"Subtitle": "Version of Nov 13, 2013",
+	"Subtitle": "Version of Jan 2, 2014",
 	"Path": "/ref/spec"
 }-->
 
@@ -5263,7 +5263,7 @@ At any time the following relationship holds:
 
 <p>
 The length of a <code>nil</code> slice, map or channel is 0.
-The capacity of a <code>nil</code> slice and channel is 0.
+The capacity of a <code>nil</code> slice or channel is 0.
 </p>
 
 <p>