Use standard compress/* packages instead of github.com/klauspost/compress/*

The reasons are:
- @klauspost optimized standard packages in go1.7+
- This removes an external dependency from fasthttp

compress.go

@@ -1,14 +1,13 @@
 package fasthttp
 
 import (
+	"compress/flate"
+	"compress/gzip"
+	"compress/zlib"
 	"fmt"
 	"io"
 	"os"
 	"sync"
-
-	"github.com/klauspost/compress/flate"
-	"github.com/klauspost/compress/gzip"
-	"github.com/klauspost/compress/zlib"
 )
 
 // Supported compression levels.

fs.go

@@ -2,6 +2,7 @@ package fasthttp
 
 import (
 	"bytes"
+	"compress/gzip"
 	"errors"
 	"fmt"
 	"html"
@@ -15,8 +16,6 @@ import (
 	"strings"
 	"sync"
 	"time"
-
-	"github.com/klauspost/compress/gzip"
 )
 
 // ServeFileBytesUncompressed returns HTTP response containing file contents