package.json: Add prepack script
package.json: Add prepack script

Add a prepack script to ensure that the package is built before
being published by the resin CI servers

Change-type: patch
Signed-off-by: Lucian Buzzo <4ccb12931fcb94d148e83438378607ae0dc0c15d@gmail.com>

resin-io-modules/resin-components,resin-io-modules/resin-components,resin-io-modules/resin-components