Update sql.go (#72)

Added a single period so that the documentation doesn't look weird. Boy, I hope the tests pass.

sql.go

@@ -9,7 +9,7 @@ import (
 	"fmt"
 )
 
-// Scan implements sql.Scanner so UUIDs can be read from databases transparently
+// Scan implements sql.Scanner so UUIDs can be read from databases transparently.
 // Currently, database types that map to string and []byte are supported. Please
 // consult database-specific driver documentation for matching types.
 func (uuid *UUID) Scan(src interface{}) error {