regexp: doc fix

This must have been from when "error" was a good variable
name for an "os.Error". But we use "err" these days.

R=golang-dev, dsymonds, r
CC=golang-dev
https://golang.org/cl/9132045

src/pkg/regexp/regexp.go

@@ -397,7 +397,7 @@ func (re *Regexp) Match(b []byte) bool {
 // MatchReader checks whether a textual regular expression matches the text
 // read by the RuneReader.  More complicated queries need to use Compile and
 // the full Regexp interface.
-func MatchReader(pattern string, r io.RuneReader) (matched bool, error error) {
+func MatchReader(pattern string, r io.RuneReader) (matched bool, err error) {
 	re, err := Compile(pattern)
 	if err != nil {
 		return false, err
@@ -408,7 +408,7 @@ func MatchReader(pattern string, r io.RuneReader) (matched bool, error error) {
 // MatchString checks whether a textual regular expression
 // matches a string.  More complicated queries need
 // to use Compile and the full Regexp interface.
-func MatchString(pattern string, s string) (matched bool, error error) {
+func MatchString(pattern string, s string) (matched bool, err error) {
 	re, err := Compile(pattern)
 	if err != nil {
 		return false, err
@@ -419,7 +419,7 @@ func MatchString(pattern string, s string) (matched bool, error error) {
 // Match checks whether a textual regular expression
 // matches a byte slice.  More complicated queries need
 // to use Compile and the full Regexp interface.
-func Match(pattern string, b []byte) (matched bool, error error) {
+func Match(pattern string, b []byte) (matched bool, err error) {
 	re, err := Compile(pattern)
 	if err != nil {
 		return false, err