build: apply gofmt from golang 1.17

lib/encoder/filename/fuzz.go

@@ -1,4 +1,5 @@
-//+build gofuzz
+//go:build gofuzz
+// +build gofuzz
 
 package filename
 

lib/encoder/filename/gentable.go

@@ -1,4 +1,5 @@
-//+build ignore
+//go:build ignore
+// +build ignore
 
 package main
 

lib/encoder/os_darwin.go

@@ -1,4 +1,5 @@
-//+build darwin
+//go:build darwin
+// +build darwin
 
 package encoder
 

lib/encoder/os_other.go

@@ -1,4 +1,5 @@
-//+build !windows,!darwin
+//go:build !windows && !darwin
+// +build !windows,!darwin
 
 package encoder
 

lib/encoder/os_windows.go

@@ -1,4 +1,5 @@
-//+build windows
+//go:build windows
+// +build windows
 
 package encoder