compress/gzip, compress/zlib: fix Writer documentation inconsistencies

Fixes #24379.

Change-Id: Ibdc763a0c2b56e26f4269f8be429880e34a2558f
Reviewed-on: https://go-review.googlesource.com/100495Reviewed-by: Joe Tsai <joetsai@google.com>

src/compress/gzip/gzip.go

@@ -41,7 +41,7 @@ type Writer struct {
 // NewWriter returns a new Writer.
 // Writes to the returned writer are compressed and written to w.
 //
-// It is the caller's responsibility to call Close on the WriteCloser when done.
+// It is the caller's responsibility to call Close on the Writer when done.
 // Writes may be buffered and not flushed until Close.
 //
 // Callers that wish to set the fields in Writer.Header must do so before

src/compress/zlib/writer.go

@@ -38,7 +38,7 @@ type Writer struct {
 // NewWriter creates a new Writer.
 // Writes to the returned Writer are compressed and written to w.
 //
-// It is the caller's responsibility to call Close on the WriteCloser when done.
+// It is the caller's responsibility to call Close on the Writer when done.
 // Writes may be buffered and not flushed until Close.
 func NewWriter(w io.Writer) *Writer {
 	z, _ := NewWriterLevelDict(w, DefaultCompression, nil)