Incorrect expected output for randomised test in JS version of kata sometimes when we have 0 koef in input.

For example,

• Input
  xz-0bz
• Expected output
  -0bz+xz
• But should be
  xz

Like it was noticed before, tests in this kata doesn't properly check for padding.
It seems that there was a problem with = symbol in tests, but now it works fine with tests like these

Test.assertEquals('this is a string!'.toBase64(), 'dGhpcyBpcyBhIHN0cmluZyE=');
Test.assertEquals('dGhpcyBpcyBhIHN0cmluZyE='.fromBase64(), 'this is a string!');

This should be better added to test cases and maybe should be noticed in description, because at the moment there are many invalid solutions are present and Base64 which they generate and parse is actualy invalid too.