doc: tweak Go 1.6 GC release notes

Go 1.6 significantly improves pause times for large heaps, but it
improves them in many other situations as well, such as when goroutine
churn is high, allocation rate is high, or when there are many
finalizers. Hence, make the statement about pause times a bit more
general.

Change-Id: Ic034b1c904c39dd1d966ee7fa96ca8bbb3614e53
Reviewed-on: https://go-review.googlesource.com/19504Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

doc/go1.6.html

@@ -248,7 +248,7 @@ Some programs may run faster, some slower.
 On average the programs in the Go 1 benchmark suite run a few percent faster in Go 1.6
 than they did in Go 1.5.
 The garbage collector's pauses are even lower than in Go 1.5,
-although the effect is likely only noticeable for programs using
+especially for programs using
 a large amount of memory.
 </p>