[JENKINS-42744] - Update WinSW to 2.0.3 and Windows Agent installer to 1.8

This PR updates WinSW to 2.0.3 in order to fix [JENKINS-42744](https://issues.jenkins-ci.org/browse/JENKINS-42744), which is reported as a critical regression in Jenkins 2.50.

Changelog: https://github.com/kohsuke/winsw/blob/master/CHANGELOG.md#203

Full diff: https://github.com/kohsuke/winsw/compare/winsw-2.0.2...winsw-2.0.3

core/pom.xml

@@ -755,7 +755,7 @@ THE SOFTWARE.
                 <artifactItem>
                   <groupId>com.sun.winsw</groupId>
                   <artifactId>winsw</artifactId>
-                  <version>2.0.2</version>
+                  <version>2.0.3</version>
                   <classifier>bin</classifier>
                   <type>exe</type>
                   <outputDirectory>${project.build.outputDirectory}/windows-service</outputDirectory>

war/pom.xml

@@ -114,7 +114,7 @@ THE SOFTWARE.
     <dependency>
       <groupId>org.jenkins-ci.modules</groupId>
       <artifactId>windows-slave-installer</artifactId>
-      <version>1.7</version>
+      <version>1.8</version>
     </dependency>
     <dependency>
       <groupId>org.jenkins-ci.modules</groupId>