doc/code.html: change 'affect' to 'effect'.

Fixes #3429.

R=golang-dev, rsc
CC=golang-dev
https://golang.org/cl/5966047

doc/code.html

@@ -236,7 +236,7 @@ are built and installed correctly.
 <p>
 As a convenience, the <code>go</code> command will assume the current directory
 if no import path is specified on the command line. This sequence of commands
-has the same affect as the one above:
+has the same effect as the one above:
 </p>
 
 <pre>