throw console warning if option[label] does not exist, prevents TypeError from breaking page

closes #155

test/unit/specs/Select.spec.js

@@ -679,6 +679,20 @@ describe('Select.vue', () => {
 			expect(vm.$children[0].$refs.toggle.querySelector('.selected-tag').textContent).toContain('Baz')
 		})
 
+		it('will console.warn when options contain objects without a valid label key', (done) => {
+			spyOn(console, 'warn')
+			const vm = new Vue({
+				template: '<div><v-select :options="[{}]"></v-select></div>',
+			}).$mount()
+			Vue.nextTick(() => {
+				expect(console.warn).toHaveBeenCalledWith(
+						'[vue-select warn]: Label key "option.label" does not exist in options object.' +
+						'\nhttp://sagalbot.github.io/vue-select/#ex-labels'
+				)
+				done()
+			})
+		})
+
 		it('should display a placeholder if the value is empty', (done) => {
 			const vm = new Vue({
 				template: '<div><v-select :options="options" placeholder="foo"></v-select></div>',