Pin libxmljs to 0.18.7 as this works on Windows

Rationale:
- Neither 0.18.6 nor 0.18.8 work on @bkimminich's Windows 10
- 0.18.7 worked on node.js 8.x and 9.x on Travis-CI and AppVeyor

Dockerfile

@@ -13,7 +13,7 @@ LABEL maintainer="Bjoern Kimminich <bjoern.kimminich@owasp.org>" \
       org.label-schema.url="http://owasp-juice.shop" \
       org.label-schema.usage="http://help.owasp-juice.shop" \
       org.label-schema.license="MIT" \
-      org.label-schema.version="7.2.2" \
+      org.label-schema.version="7.2.3" \
       org.label-schema.docker.cmd="docker run --rm -p 3000:3000 bkimminich/juice-shop" \
       org.label-schema.docker.params="NODE_ENV=string name of the custom configuration,CTF_KEY=string key to hash challenges into CTF flag codes" \
       org.label-schema.vcs-url="https://github.com/bkimminich/juice-shop.git" \

app/package.json

 {
   "name": "juice-shop-angular",
-  "version": "7.2.2",
+  "version": "7.2.3",
   "private": true,
   "dependencies": {
     "angular": "~1.6.9",

package.json

 {
   "name": "juice-shop",
-  "version": "7.2.2",
+  "version": "7.2.3",
   "description": "An intentionally insecure JavaScript Web Application",
   "homepage": "http://owasp-juice.shop",
   "author": "Björn Kimminich <bjoern.kimminich@owasp.org> (https://www.owasp.org/index.php/User:Bjoern_Kimminich)",
@@ -81,7 +81,7 @@
     "js-yaml": "~3.11.0",
     "jsonwebtoken": "~8.2",
     "jssha": "~2.3",
-    "libxmljs": "0.18.6",
+    "libxmljs": "0.18.7",
     "marsdb": "~0.6",
     "morgan": "~1.9",
     "multer": "~1.3",