Update _index.en.md

Updating docker container that gets pulled upon first invocation.

To line up with https://cicd.serverlessworkshops.io/sam/init.html

`Choose nodejs12.x for runtime`

Author: carltondickson

workshop/content/local/run/_index.en.md

@@ -46,4 +46,4 @@ In Cloud9, go to the top menu and chose **Tools > Preview > Preview Running Appl
 
 ![PreviewSamLocal](/images/screenshot-samlocal-preview.png)
 
-Note how SAM is pulling the Docker container image _lambci/lambda:nodejs10.x_ automatically. This is how SAM is able to simulate the Lambda runtime locally and run your function within it. The first invocation might take a few seconds due to the docker pull command, but subsequent invocations should be much faster.
+Note how SAM is pulling the Docker container image _lambci/lambda:nodejs12.x_ automatically. This is how SAM is able to simulate the Lambda runtime locally and run your function within it. The first invocation might take a few seconds due to the docker pull command, but subsequent invocations should be much faster.