Fix Button Interface Typings

[alex-osman]

Issue

Fixes #763: Button typings were not full

Solution

Added typings for all valid combinations.

Allows for variations of the following:

swal({
  buttons: [true, true],                              // booleans
  buttons: ['Stay on this page', 'Continue'],         // strings
  buttons: [true, 'Delete'],                          // both

  buttons: {                                          // ButtonList
    cancel: true,                                     // boolean
    confirm: {                                        // ButtonOptions
      ....
    }
  }
})

[Klerith]

Please made this changes I am getting the same issue on TypeScript

[alex-osman]

bump @t4t5

[t4t5]

Thx!