small correction to Query URL manipulation JS (related to #117)

ippisite/ippidb/static/js/ippidb-query-url.js

@@ -11,7 +11,7 @@ class QueryUrl {
             this.url.searchParams.delete(paramName);
             paramValue.forEach(function(value) {
                 this.url.searchParams.append(paramName, value);
-            });
+            }.bind(this));
         } else if (paramValue != null) {
             // set one value for one parameter
             this.url.searchParams.set(paramName, paramValue);
@@ -19,7 +19,7 @@ class QueryUrl {
             // unset value for multiple parameters
             paramName.forEach(function(name) {
                 this.url.searchParams.delete(name);
-            });
+            }.bind(this));
         } else {
             // unset value for one parameter
             this.url.searchParams.delete(paramName);