container/heap: fix comments style

Fixes golint warning about comment on exported function.

Change-Id: Ia6a910e2dca2cd31d8de64419e36add6191e804d
Reviewed-on: https://go-review.googlesource.com/105495Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

src/container/heap/heap.go

@@ -18,7 +18,9 @@ package heap
 
 import "sort"
 
-// Any type that implements heap.Interface may be used as a
+// The Interface type describes the requirements
+// for a type using the routines in this package.
+// Any type that implements it may be used as a
 // min-heap with the following invariants (established after
 // Init has been called or if the data is empty or sorted):
 //
@@ -33,11 +35,10 @@ type Interface interface {
 	Pop() interface{}   // remove and return element Len() - 1.
 }
 
-// A heap must be initialized before any of the heap operations
-// can be used. Init is idempotent with respect to the heap invariants
+// Init establishes the heap invariants required by the other routines in this package.
+// Init is idempotent with respect to the heap invariants
 // and may be called whenever the heap invariants may have been invalidated.
 // Its complexity is O(n) where n = h.Len().
-//
 func Init(h Interface) {
 	// heapify
 	n := h.Len()