add ssr support

[Sitronik]

When I import vue-slick I get this error in ssr:

ReferenceError: window is not defined
    at /Users/denis/Documents/projects/project/node_modules/vue-slick/dist/slickCarousel.cjs.js:245:17
    at /Users/denis/Documents/projects/project/node_modules/vue-slick/dist/slickCarousel.cjs.js:241:26
    at /Users/denis/Documents/projects/project/node_modules/vue-slick/dist/slickCarousel.cjs.js:244:2
    at createCommonjsModule (/Users/denis/Documents/projects/project/node_modules/vue-slick/dist/slickCarousel.cjs.js:235:35)
    at Object.<anonymous> (/Users/denis/Documents/projects/project/node_modules/vue-slick/dist/slickCarousel.cjs.js:238:13)
    at Module._compile (internal/modules/cjs/loader.js:759:30)
    at Module._compile (/Users/denis/Documents/projects/project/node_modules/pirates/lib/index.js:99:24)
    at Module._extensions..js (internal/modules/cjs/loader.js:770:10)
    at Object.newLoader [as .js] (/Users/denis/Documents/projects/project/node_modules/pirates/lib/index.js:104:7)
    at Module.load (internal/modules/cjs/loader.js:628:32)
    at Function.Module._load (internal/modules/cjs/loader.js:555:12)
    at Module.require (internal/modules/cjs/loader.js:666:19)
    at require (internal/modules/cjs/helpers.js:16:16)
    at r (/Users/denis/Documents/projects/project/node_modules/vue-server-renderer/build.dev.js:9315:16)
    at eval (webpack-internal:///vue-slick:1:18)
    at Object.vue-slick (main.js:1325:1)

And in client:
500 | Internal Server Error

Fixed it all, please merge