Add back exec-maven-plugin

pom.xml

@@ -228,6 +228,33 @@
                 <artifactId>maven-surefire-plugin</artifactId>
                 <version>3.2.2</version>
             </plugin>
+            <plugin>
+                <!--
+                    We need this for updating the submodule during release. Maven SCM
+                    doesn't support this itself apparently. See
+                    https://github.com/apache/maven-scm/pull/179
+                -->
+                <groupId>org.codehaus.mojo</groupId>
+                <artifactId>exec-maven-plugin</artifactId>
+                <!--
+                    We are using 3.0.0 as 3.1.1 fails due to this issue:
+                    https://github.com/mojohaus/exec-maven-plugin/issues/373
+                -->
+                <version>3.0.0</version>
+                <executions>
+                    <execution>
+                        <phase>initialize</phase>
+                        <id>invoke build</id>
+                        <goals>
+                            <goal>exec</goal>
+                        </goals>
+                    </execution>
+                </executions>
+                <configuration>
+                    <executable>git</executable>
+                    <commandlineArgs>submodule update --init --recursive</commandlineArgs>
+                </configuration>
+            </plugin>
             <plugin>
                 <groupId>org.codehaus.mojo</groupId>
                 <artifactId>versions-maven-plugin</artifactId>