go.mod: set go version to go1.9 (#1055)

neild · web-flow · commit 84668698ea25 · 2020-03-12T15:07:03.000-07:00
diff --git a/go.mod b/go.mod
@@ -1,3 +1,3 @@
 module github.com/golang/protobuf
 
-go 1.12
+go 1.9

Original file line number	Diff line number	Diff line change
`@@ -1,3 +1,3 @@`
`1`	`1`	`module github.com/golang/protobuf`
`2`	`2`
`3`		`-go 1.12`
	`3`	`+go 1.9`