Upgrade dependencies

[yuya-oc]

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Summary
Upgrade dependencies.

After this PR, we will get ready to switch back to npm.

Issue link
#898

Test Cases

• Apps should normally work.
• "Save Image" context menu should work.

Additional Notes
https://circleci.com/gh/yuya-oc/desktop/1187#artifacts

[yuya-oc]

Looks good to me.

• Windows 10 Pro 64-bit (zip, exe)
• macOS 10.14.1 (zip, dmg)

[yuya-oc]

Rebased against the latest master branch.

Artifacts: https://circleci.com/gh/yuya-oc/desktop/1211#artifacts

[yuya-oc]

Added Electron v4. As far as reading the release notes, I could not find critical changes for us (However v5 will break the app due to default webPreferences values).
https://electronjs.org/releases#4.0.0

Artifacts: https://circleci.com/gh/yuya-oc/desktop/1215#artifacts

[wget]

The build succeeded on my Windows 10 Pro x64 1809 dev machine.

The build succeeded on AppVeyor as well BUT only 1 test is failing. Could we please fix this before merging this pull request?

Here are the AppVeyor logs with the details of the failing test: https://ci.appveyor.com/project/wget/mattermost-desktop/builds/21360791

Also, for a reason I don't know (even if this is NOT a regression) I realized the GUI on Windows was blurry compared to the web ui on the left:

I checked by disabling the GPU rendering, but without any improvement. Are we aware of this issue? Is a dedicated bug report already open?

[yuya-oc]

@wget Updated the branch. What about this?

For blurry rendering, I think it's known issue (#560, electron/electron#10025). The reason is that Electron's webview unexpectedly uses grayscale antialiasing. It looks like blurry.

[wget]

@yuya-oc Everything worked like expected. The migration from yarn to npm went smoothly. All tests passed.

Artefacts: https://ci.appveyor.com/project/wget/mattermost-desktop/builds/21505020

It's finally time to merge!