context: fix references to "d" in WithDeadline docs

Docs of WithDeadline refers to variable "d" which does not exist
in the docs.

This commit renames the time argument to "d" to make the doc work.

Change-Id: Ifd2c1be7d2e3f7dfb21cd9bb8ff7fc5039c8d3bd
Reviewed-on: https://go-review.googlesource.com/65130
Run-TryBot: Ian Lance Taylor <iant@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>

src/context/context.go

@@ -380,25 +380,25 @@ func (c *cancelCtx) cancel(removeFromParent bool, err error) {
 //
 // Canceling this context releases resources associated with it, so code should
 // call cancel as soon as the operations running in this Context complete.
-func WithDeadline(parent Context, deadline time.Time) (Context, CancelFunc) {
-	if cur, ok := parent.Deadline(); ok && cur.Before(deadline) {
+func WithDeadline(parent Context, d time.Time) (Context, CancelFunc) {
+	if cur, ok := parent.Deadline(); ok && cur.Before(d) {
 		// The current deadline is already sooner than the new one.
 		return WithCancel(parent)
 	}
 	c := &timerCtx{
 		cancelCtx: newCancelCtx(parent),
-		deadline:  deadline,
+		deadline:  d,
 	}
 	propagateCancel(parent, c)
-	d := time.Until(deadline)
-	if d <= 0 {
+	dur := time.Until(d)
+	if dur <= 0 {
 		c.cancel(true, DeadlineExceeded) // deadline has already passed
 		return c, func() { c.cancel(true, Canceled) }
 	}
 	c.mu.Lock()
 	defer c.mu.Unlock()
 	if c.err == nil {
-		c.timer = time.AfterFunc(d, func() {
+		c.timer = time.AfterFunc(dur, func() {
 			c.cancel(true, DeadlineExceeded)
 		})
 	}