Turn dependency peer requirements from error to warning during build

[bdiz]

Describe the bug
When a dependency of your project has a peer dependency in their package.json and npm thinks it is not installed vcp-electron-builder errors out on build.

npm install just prints a warning but still builds fine.

To Reproduce

vue create my-app
cd my-app
npm install --save-dev [email protected]
vue invoke vue-cli-plugin-electron-builder
npm install --save [email protected] @firebase/app
npm run build
# npm WARN [email protected] requires a peer of firebase@>= 4.0.0 but none is installed. You must install peer dependencies yourself.
# build succeeds
npm run build:electron
# Unhandled rejection Error: Unresolved node modules: firebase
# build fails

Expected behavior
I expect a warning peer dependencies like npm run build and the build to succeed.

Environment (please complete the following information):

• OS and version: Ubuntu 16.10
• Node version: v10.5.0
• npm version: 6.1.0
• yarn version (if used):
• vue-cli-plugin-electron-builder version : 1.0.0-beta-5
• vue/cli-service: 3.0.0-rc.3
• other vue plugins used: none
• custom config for vcp-electron-builder: none
• (if possible) link to your repo: not possible

Additional context
I install firebase using @firebase/app to save on bundle size when built for web. This is why I get the warning with npm run build but my app will still function properly.

I actually don't use firebase for electron builds and instead use an on disk db which really makes this warning unimportant to me for electron builds.

[nklayman]

For some reason, my build works completely fine after following your reproduction instructions. I am on windows though, so that might be why. I am going camping for two weeks starting later today, so I will not be able to help after 1:30ish pacific time. You might have to figure this one out on your own.

[nklayman]

I believe this issue was fixed in electron-builder. I will close this issue, if it still fails feel free to re-open it.