Merge pull request #1353 from urfave/drop-go111module

Drop references/usage of GO111MODULE

README.md

@@ -30,7 +30,7 @@ Go Modules are required when using this package. [See the go blog guide on using
 ### Using `v2` releases
 
 ```
-$ GO111MODULE=on go get github.com/urfave/cli/v2
+$ go get github.com/urfave/cli/v2
 ```
 
 ```go
@@ -44,7 +44,7 @@ import (
 ### Using `v1` releases
 
 ```
-$ GO111MODULE=on go get github.com/urfave/cli
+$ go get github.com/urfave/cli
 ```
 
 ```go