archive/zip: fix UncompressedSize godoc

Change-Id: I0c142eb18af7b03759041e894bbce0f365ea9d7e
Reviewed-on: https://go-review.googlesource.com/c/go/+/588116
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Dmitri Shuralyov <dmitshur@google.com>
Auto-Submit: Ian Lance Taylor <iant@google.com>
Reviewed-by: Ian Lance Taylor <iant@google.com>

src/archive/zip/struct.go

@@ -143,9 +143,9 @@ type FileHeader struct {
 	// Deprecated: Use CompressedSize64 instead.
 	CompressedSize uint32
 
-	// UncompressedSize is the compressed size of the file in bytes.
+	// UncompressedSize is the uncompressed size of the file in bytes.
 	// If either the uncompressed or compressed size of the file
-	// does not fit in 32 bits, CompressedSize is set to ^uint32(0).
+	// does not fit in 32 bits, UncompressedSize is set to ^uint32(0).
 	//
 	// Deprecated: Use UncompressedSize64 instead.
 	UncompressedSize uint32