Fix/env vars rest dial (#1225)

* rest dial needs to support env vars

* wip

lib/tasks/rest_dial.js

@@ -77,6 +77,7 @@ class TaskRestDial extends Task {
       const httpHeaders = b3 && {b3};
       const params = {
         ...(cs.callInfo.toJSON()),
+        ...(this.env_vars && {env_vars: this.env_vars}),
         defaults: {
           synthesizer: {
             vendor: cs.speechSynthesisVendor,