ensure options.initial is handled properly when defined as a function

Pointed out here: #295

lib/prompts/toggle.js

@@ -5,7 +5,7 @@ const BooleanPrompt = require('../types/boolean');
 class TogglePrompt extends BooleanPrompt {
   async initialize() {
     await super.initialize();
-    this.value = this.initial = !!this.options.initial;
+    this.value = this.initial = this.resolve(this.options.initial);
     this.disabled = this.options.disabled || 'no';
     this.enabled = this.options.enabled || 'yes';
     await this.render();

test/promt.toggle.js → test/prompt.toggle.js

@@ -32,6 +32,34 @@ describe('toggle', function() {
           assert.equal(answer, true);
         });
     });
+
+    it('toggle should call options.initial when a function is defined (false)', () => {
+      prompt = new Prompt({
+        message: 'prompt-toggle',
+        initial: () => false
+      });
+
+      prompt.once('run', () => prompt.submit());
+
+      return prompt.run()
+        .then(answer => {
+          assert.equal(answer, false);
+        });
+    });
+
+    it('toggle should call options.initial when a function is defined (true)', () => {
+      prompt = new Prompt({
+        message: 'prompt-toggle',
+        initial: () => true
+      });
+
+      prompt.once('run', () => prompt.submit());
+
+      return prompt.run()
+        .then(answer => {
+          assert.equal(answer, true);
+        });
+    });
   });
 
   describe('key handling', () => {