unicode: fix doc comment for Range32

R=golang-dev, r
CC=golang-dev
https://golang.org/cl/4811050

src/pkg/unicode/letter.go

@@ -32,7 +32,7 @@ type Range16 struct {
 }
 
 // Range32 represents of a range of Unicode code points and is used when one or
-//  more of the values will not fit in 16 bits.  The range runs from Lo to Hi
+// more of the values will not fit in 16 bits.  The range runs from Lo to Hi
 // inclusive and has the specified stride. Lo and Hi must always be >= 1<<16.
 type Range32 struct {
 	Lo     uint32