fix naked < as reported by pwil3058@gmail.com

R=rsc
CC=pwil3058
https://golang.org/cl/174087

doc/go_tutorial.html

@@ -355,7 +355,7 @@ By the way, another thing that works on strings, arrays, slices, maps
 and channels is the <code>range</code> clause on <code>for</code> loops.  Instead of writing
 <p>
 <pre>
-    for i := 0; i < len(a); i++ { ... }
+    for i := 0; i &lt; len(a); i++ { ... }
 </pre>
 <p>
 to loop over the elements of a slice (or map or ...) , we could write

doc/go_tutorial.txt

@@ -278,7 +278,7 @@ slices, maps, and channels.
 By the way, another thing that works on strings, arrays, slices, maps
 and channels is the "range" clause on "for" loops.  Instead of writing
 
-	for i := 0; i < len(a); i++ { ... }
+	for i := 0; i &lt; len(a); i++ { ... }
 
 to loop over the elements of a slice (or map or ...) , we could write