remove string ref

Author: bevali

dist/index.js

@@ -356,6 +356,9 @@
             });
           });
         }
+      }, {
+        key: 'ref',
+        value: {}
       }, {
         key: 'render',
         value: function render() {
@@ -370,7 +373,7 @@
             { style: containerStyles, className: this.props.className },
             _react2.default.createElement(
               'div',
-              { style: style, ref: 'map' },
+              { style: style, ref: (element) => (this.ref.map = element) },
               'Loading map...'
             ),
             this.renderChildren()