sort: change let to let's

Trivial typo

Change-Id: I3804f365519453bfa19997f55ead34742ac1a9db
GitHub-Last-Rev: 0e04e928d05121099b78a2cefc1cb7531f6a7650
GitHub-Pull-Request: golang/go#29930
Reviewed-on: https://go-review.googlesource.com/c/159479Reviewed-by: Emmanuel Odeke <emm.odeke@gmail.com>

src/sort/sort.go

@@ -131,7 +131,7 @@ func doPivot(data Interface, lo, hi int) (midlo, midhi int) {
 		c--
 	}
 	// If hi-c<3 then there are duplicates (by property of median of nine).
-	// Let be a bit more conservative, and set border to 5.
+	// Let's be a bit more conservative, and set border to 5.
 	protect := hi-c < 5
 	if !protect && hi-c < (hi-lo)/4 {
 		// Lets test some points for equality to pivot