Fix Dockerfile to be able to test swagger spec

Change-Id: I4b42de41a5d03d6e8627f33e84a5dd810aff6a24
Signed-off-by: garciadeblas <gerardo.garciadeblas@telefonica.com>
diff --git a/Dockerfile b/Dockerfile
index 2760e73..8cc0a7d 100644
--- a/Dockerfile
+++ b/Dockerfile
@@ -18,6 +18,8 @@
 FROM ubuntu:18.04
 
 RUN apt-get update && apt-get install -y git build-essential nodejs npm
+RUN npm install -g npm@latest
+RUN npm install --save @openapi-contrib/json-schema-to-openapi-schema
 RUN npm install -g swagger-cli
 RUN npm install -g speccy