Fix env variables to include existing environment variables, then ove…

…rride.

src/exec_auth.ts

@@ -53,7 +53,7 @@ export class ExecAuth implements Authenticator {
         }
         let opts: shell.ExecOpts;
         if (exec.env) {
-            const env = {};
+            const env = process.env;
             exec.env.forEach((elt) => (env[elt.name] = elt.value));
             opts = { env };
         }