database/sql: fix outdated package name in doc.txt

Change-Id: I4417c5a8537095a6464ce919b2e5cb250e179939
Reviewed-on: https://go-review.googlesource.com/47332Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

src/database/sql/doc.txt

@@ -31,7 +31,7 @@ Goals of the sql and sql/driver packages:
 * Handle concurrency well.  Users shouldn't need to care about the
   database's per-connection thread safety issues (or lack thereof),
   and shouldn't have to maintain their own free pools of connections.
-  The 'db' package should deal with that bookkeeping as needed.  Given
+  The 'sql' package should deal with that bookkeeping as needed.  Given
   an *sql.DB, it should be possible to share that instance between
   multiple goroutines, without any extra synchronization.