style(Field): update disabled color (#6534)

src/field/index.js

@@ -577,6 +577,7 @@ export default createComponent({
         arrowDirection={this.arrowDirection}
         class={bem({
           error: this.showError,
+          disabled: this.disabled,
           [`label-${labelAlign}`]: labelAlign,
           'min-height': this.type === 'textarea' && !this.autosize,
         })}

src/field/index.less

@@ -1,6 +1,10 @@
 @import '../style/var';
 
 .van-field {
+  &--disabled {
+    color: @field-disabled-text-color;
+  }
+
   &__label {
     flex: none;
     box-sizing: border-box;

src/field/test/__snapshots__/demo.spec.js.snap

@@ -51,7 +51,7 @@ exports[`renders demo correctly 1`] = `
         <div class="van-field__body"><input type="text" readonly="readonly" class="van-field__control"></div>
       </div>
     </div>
-    <div class="van-cell van-field">
+    <div class="van-cell van-field van-field--disabled">
       <div class="van-cell__title van-field__label"><span>文本</span></div>
       <div class="van-cell__value van-field__value">
         <div class="van-field__body"><input type="text" disabled="disabled" class="van-field__control"></div>