remove multiple selection height property

build/less/select2.less

@@ -76,7 +76,6 @@
   .select2-selection--multiple {
     border: 1px solid @gray;
     border-radius: @input-radius;
-    height: 34px;
     &:focus {
       border-color: @light-blue;
     }
@@ -100,4 +99,4 @@
 }
 .select2-container .select2-selection--single .select2-selection__rendered {
   padding-right: 10px;
-}
+}