[clang-tidy] use override instead of virtual

Found with modernize-use-override

Signed-off-by: Rosen Penev <rosenp@gmail.com>

src/fs/io/AutoGunzipReader.hxx

@@ -40,7 +40,7 @@ public:
 	~AutoGunzipReader() noexcept;
 
 	/* virtual methods from class Reader */
-	virtual size_t Read(void *data, size_t size) override;
+	size_t Read(void *data, size_t size) override;
 
 private:
 	void Detect();

src/fs/io/PeekReader.hxx

@@ -43,7 +43,7 @@ public:
 	const void *Peek(size_t size);
 
 	/* virtual methods from class Reader */
-	virtual size_t Read(void *data, size_t size) override;
+	size_t Read(void *data, size_t size) override;
 };
 
 #endif