chore: wrong import

Author: crisbeto

src/lib/core/option/option.ts

@@ -12,7 +12,7 @@ import {
 import {CommonModule} from '@angular/common';
 import {ENTER, SPACE} from '../keyboard/keycodes';
 import {coerceBooleanProperty} from '../coercion/boolean-property';
-import {MdRippleModule} from '../ripple/ripple';
+import {MdRippleModule} from '../ripple/index';
 import {MdSelectionModule} from '../selection/index';
 
 /**