add boolean entry for env

yargs/yargs-tests.ts

@@ -156,6 +156,7 @@ function Argv$env() {
 	var argv = yargs
 		.env('YARGS_PREFIX_')
 		.env()
+		.env(true);
 }
 
 function Argv$array() {

yargs/yargs.d.ts

@@ -95,6 +95,7 @@ declare module "yargs" {
 			help(option: string, description?: string): Argv;
 			
 			env(prefix?: string): Argv;
+			env(enable: boolean): Argv;
 
 			epilog(msg: string): Argv;
 			epilogue(msg: string): Argv;