Fix check-pruned-shrinkwrap script

Author: dpgraham

check-pruned-shrinkwrap.js

@@ -6,8 +6,13 @@ const path = require('path');
 const log = new logger.getLogger('ShrinkwrapValidator');
 
 async function main () {
+  const shrinkwrapPath = path.resolve('npm-shrinkwrap.json');
+  if (!(await fs.exists(shrinkwrapPath))) {
+    log.info('No shrinkwrap found. Skipping shrinkwrap check');
+    return;
+  }
+  const shrinkwrap = JSON.parse(await fs.readFile(shrinkwrapPath));
   const backupShrinkwrap = JSON.parse(await fs.readFile(path.resolve('npm-shrinkwrap-backup.json')));
-  const shrinkwrap = JSON.parse(await fs.readFile(path.resolve('npm-shrinkwrap.json')));
   log.info('Checking that pruned shrinkwrap is a subset of primary shrinkwrap');
   if (!_.isMatch(backupShrinkwrap, shrinkwrap)) {
     log.errorAndThrow('Pruned shrinkwrap (shrinkwrap with dev dependencies removed) is not a subset of the original npm-shrinkwrap.json');