Update old files so they can be zipped

CodeBuild was giving me an error like:

> [Container] 2020/09/21 18:50:44 Entering phase BUILD
> [Container] 2020/09/21 18:50:44 Running command aws cloudformation
> package --template template.yml --s3-bucket $S3_BUCKET --output-template \
> template-export.yml
> Unable to upload artifact None referenced by CodeUri parameter of
> HelloWorld resource.
> ZIP does not support timestamps before 1980

This implements [a
workaround](aws/aws-cli#2639 (comment)),
slightly adapted. The command

find node_modules/ -mtime +14600 -print

revealed that some files within node_modules/@babel and
node_modules/babel-preset-current-node-syntax were very old.

buildspec.yml

@@ -16,6 +16,10 @@ phases:
       - npm test
   build:
     commands:
+      # Update the age of old files
+      # Some packages can bring in old files, causing the error:
+      # ZIP does not support timestamps before 1980
+      - find node_modules/ -mtime +14600 -exec touch {} +
       # Use AWS SAM to package the application using AWS CloudFormation
       - aws cloudformation package --template template.yml --s3-bucket $S3_BUCKET --output-template template-export.yml