Update go.mod (#34)

C. Brown · vishr · commit d700b06ce5f7 · 2019-06-09T23:34:36.000-07:00
The go 1.13 directive makes this incompatible with the latest stable go.
diff --git a/go.mod b/go.mod
@@ -9,4 +9,4 @@ require (
 	golang.org/x/sys v0.0.0-20190602015325-4c4f7f33c9ed // indirect
 )
 
-go 1.13
+go 1.12

Original file line number	Diff line number	Diff line change
`@@ -9,4 +9,4 @@ require (`
`9`	`9`	`golang.org/x/sys v0.0.0-20190602015325-4c4f7f33c9ed // indirect`
`10`	`10`	`)`
`11`	`11`
`12`		`-go 1.13`
	`12`	`+go 1.12`