all: use go:build directives

Signed-off-by: Sebastien Binet <binet@cern.ch>

Author: sbinet

py/gen.go

@@ -2,6 +2,7 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
+//go:build ignore
 // +build ignore
 
 package main

py/range_repr110.go

@@ -2,7 +2,9 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
+//go:build go1.10
 // +build go1.10
+
 // Range object
 
 package py

py/range_repr19.go

@@ -2,7 +2,9 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
+//go:build !go1.10
 // +build !go1.10
+
 // Range object
 
 package py

repl/web/serve.go

@@ -1,4 +1,5 @@
-//+build none
+//go:build none
+// +build none
 
 package main