Bump node and serverless versions (#34)

* Bump node and sls versions

* Omit version

Co-authored-by: Davide Violante <DavideViolante@users.noreply.github.com>

Author: drieshooghe

Dockerfile

@@ -1,4 +1,4 @@
-FROM node:10-slim
+FROM node:12-slim
 
 
 LABEL version="1.0.0"
@@ -11,5 +11,5 @@ LABEL "com.github.actions.description"="Wraps the Serverless Framework to enable
 LABEL "com.github.actions.icon"="zap"
 LABEL "com.github.actions.color"="red"
 
-RUN npm i -g serverless@1.54.0
+RUN npm i -g serverless
 ENTRYPOINT ["serverless"]