spec: change the wording regarding select statement choice

s/pseudo-random fair/uniform pseudo-random/
This careful word choice soothes the theoretically inclined.

R=golang-dev, rsc, gri
CC=golang-dev
https://golang.org/cl/5528098

doc/go_spec.html

 <!-- title The Go Programming Language Specification -->
-<!-- subtitle Version of January 9, 2012 -->
+<!-- subtitle Version of January 13, 2012 -->
 
 <!--
 TODO
@@ -4240,7 +4240,7 @@ effects in that evaluation will occur for all the communications
 in the "select" statement.
 </p>
 <p>
-If multiple cases can proceed, a pseudo-random fair choice is made to decide
+If multiple cases can proceed, a uniform pseudo-random choice is made to decide
 which single communication will execute.
 <p>
 The receive case may declare one or two new variables using a