Remove runtime polyfill

[pavelvlasov]

Related to #5

[yonatanmn]

But now you are depending on native support for babel's runtime.
Please add to you PR some polyfills (that will work on old browsers)

[pavelvlasov]

@yonatanmn I think it make sense to let a developer make decision about what polyfill to use on compilation stage. Isn't it?

[yonatanmn]

the repo shouid be distributed with no need for outside dependencies.
I guess the build should be corrected, so it won't rely on babel's runtime.
An easy solution is just remove this dependency and add keys and assign as utils