database/sql: correctly spell constants

Also add a link to more information about isolation levels as defined by the
SQL standard. Fixes #17682.

Change-Id: I94c53b713f4c882af40cf15fe5f1e5dbc53ea741
Reviewed-on: https://go-review.googlesource.com/32418Reviewed-by: Daniel Theophanes <kardianos@gmail.com>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>

src/database/sql/sql.go

@@ -97,11 +97,13 @@ type IsolationLevel int
 
 // Various isolation levels that drivers may support in BeginContext.
 // If a driver does not support a given isolation level an error may be returned.
+//
+// See https://en.wikipedia.org/wiki/Isolation_(database_systems)#Isolation_levels.
 const (
 	LevelDefault IsolationLevel = iota
-	LevelReadUncommited
-	LevelReadCommited
-	LevelWriteCommited
+	LevelReadUncommitted
+	LevelReadCommitted
+	LevelWriteCommitted
 	LevelRepeatableRead
 	LevelSnapshot
 	LevelSerializable