fixed spelling (#156)

errors.go

@@ -192,7 +192,7 @@ func Wrap(err error, message string) error {
 }
 
 // Wrapf returns an error annotating err with a stack trace
-// at the point Wrapf is call, and the format specifier.
+// at the point Wrapf is called, and the format specifier.
 // If err is nil, Wrapf returns nil.
 func Wrapf(err error, format string, args ...interface{}) error {
 	if err == nil {