feat(Form): add colon prop

src/form/test/__snapshots__/props.spec.js.snap

@@ -1,5 +1,22 @@
 // Jest Snapshot v1, https://goo.gl/fbAQLP
 
+exports[`colon prop 1`] = `
+<form class="van-form">
+  <div class="van-cell van-field">
+    <div class="van-cell__title van-field__label"><span>Label:</span></div>
+    <div class="van-cell__value van-field__value">
+      <div class="van-field__body"><input type="text" class="van-field__control"></div>
+    </div>
+  </div>
+  <div class="van-cell van-field">
+    <div class="van-cell__title van-field__label">Custom Label:</div>
+    <div class="van-cell__value van-field__value">
+      <div class="van-field__body"><input type="text" class="van-field__control"></div>
+    </div>
+  </div>
+</form>
+`;
+
 exports[`error-message-align prop 1`] = `
 <form class="van-form">
   <div class="van-cell van-field">

src/form/test/props.spec.js

@@ -105,6 +105,20 @@ test('validate-first prop', async () => {
   expect(onSubmit).toHaveBeenCalledWith({ A: 'foo', B: 'foo' });
 });
 
+test('colon prop', () => {
+  const wrapper = mountForm({
+    template: `
+      <van-form colon>
+        <van-field label="Label" />
+        <van-field>
+          <template #label>Custom Label</template>
+        </van-field>
+      </van-form>
+    `,
+  });
+  expect(wrapper).toMatchSnapshot();
+});
+
 test('label-align prop', () => {
   const wrapper = mountForm({
     template: `