Invalid calling object 'btoa' in IE11

[kyemelianov]

We an issue in IE11 after build product version.
It is described and resolved in PR70
IE11 can't use 'btoa' without window context.
It is easy reproduce in IE11:
({ btoa: window.btoa }).btoa('123') - return Error

[postatum]

Closed via #150

[postatum]

The fix is now released in version 4.3.2. Thank you for the report!