Remove unnecessary defer in Encoder.EncodeKeyval.

This change results in a nice speed improvement for a method that is
normally called within a loop.

name            old time/op    new time/op    delta
EncodeKeyval-4    1.74µs ± 1%    1.46µs ± 1%  -16.39%    (p=0.000 n=10+9)

encode.go

@@ -63,7 +63,7 @@ var (
 // single space is written before the second and subsequent keys in a record.
 // Nothing is written if a non-nil error is returned.
 func (enc *Encoder) EncodeKeyval(key, value interface{}) error {
-	defer enc.scratch.Reset()
+	enc.scratch.Reset()
 	if enc.needSep {
 		if _, err := enc.scratch.Write(space); err != nil {
 			return err

encode_test.go

@@ -4,6 +4,7 @@ import (
 	"bytes"
 	"errors"
 	"fmt"
+	"io/ioutil"
 	"reflect"
 	"testing"
 	"time"
@@ -187,3 +188,12 @@ type errorMarshaler struct{}
 func (errorMarshaler) MarshalText() ([]byte, error) {
 	return nil, marshalError
 }
+
+func BenchmarkEncodeKeyval(b *testing.B) {
+	b.ReportAllocs()
+	enc := logfmt.NewEncoder(ioutil.Discard)
+	for i := 0; i < b.N; i++ {
+		enc.EncodeKeyval("sk", "10")
+		enc.EncodeKeyval("some-key", "a rather long string with spaces")
+	}
+}