Update parent 12 (#55)

pom.xml

@@ -1,11 +1,9 @@
 <?xml version="1.0" encoding="UTF-8"?>
 <!--
-
     Copyright (c) 2020, RTE (http://www.rte-france.com)
     This Source Code Form is subject to the terms of the Mozilla Public
     License, v. 2.0. If a copy of the MPL was not distributed with this
     file, You can obtain one at http://mozilla.org/MPL/2.0/.
-
 -->
 <project xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd"
          xmlns="http://maven.apache.org/POM/4.0.0"
@@ -15,7 +13,7 @@
     <parent>
         <groupId>com.powsybl</groupId>
         <artifactId>powsybl-parent-ws</artifactId>
-        <version>11</version>
+        <version>12</version>
         <relativePath/>
     </parent>