feat: use 7za to produce Squirrel.mac zip (smaller size — the same ti…

[develar]

…me to compress)

Also, add compression option to set compression level in one place (currently, only Linux and OS X supported)

[asethwright]

Is there a dependency requirement for 7za I'm missing? I am getting errors on my build.

Packaging app for platform darwin x64 using electron v0.37.3
App is not signed: CSC_LINK or CSC_NAME are not specified
Creating DMG
Creating ZIP for Squirrel.Mac
.../node_modules/electron-builder/vendor/osx/7za: line 1: version: command not found
.../node_modules/electron-builder/vendor/osx/7za: line 2: oid: command not found
/Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/size: 1667792: No such file or directory.

[asethwright]

I tried brew install p7zip

which 7za
/usr/local/bin/7za

Will be glad to open an issue if needed. Thanks for your time. This makes building so easy.

[develar]

@asethwright #296

[asethwright]

Ah, thanks!