fix(build): support package.json without 'dependencies' field (#828)

Co-authored-by: Noah Klayman <[email protected]>

Author: cawa-93

index.js

@@ -157,7 +157,7 @@ module.exports = (api, options) => {
         const externals = getExternals(api, pluginOptions)
         // https://github.com/nklayman/vue-cli-plugin-electron-builder/issues/223
         // Strip non-externals from dependencies so they won't be copied into app.asar
-        Object.keys(pkg.dependencies).forEach((dependency) => {
+        Object.keys(pkg.dependencies || {}).forEach((dependency) => {
           if (!Object.keys(externals).includes(dependency)) {
             delete pkg.dependencies[dependency]
           }