Add this code to the Custom CSS field on the Style tab of your Reviews widget’s settings:
.es-header-rating-reviews-count::after {
content: 'reviews)';
position: relative;
right: 4px;
bottom: -1px;
padding-left: 2px;
line-height: 14px;
background-color: #F8F8F8;
font-size: 12px;
}