Fixed quotes in Jenkinsfile

Change-Id: I53657284447b7cf7f3dd2e88947f4edd1b991c23
diff --git a/Jenkinsfile b/Jenkinsfile
index 3cbef8a..b9eccb6 100644
--- a/Jenkinsfile
+++ b/Jenkinsfile
@@ -41,7 +41,7 @@
                 sh 'docker stop xos-gui'
                 sh 'docker rm xos-gui'
                 sh 'docker rmi xosproject/xos-gui'
-                sh 'docker rmi $(docker images | grep none | awk '{print $3}')'
+                sh 'docker rmi $(docker images | grep none | awk "{print $3}")'
             }
             echo "RESULT: ${currentBuild.result}"
        }