Bug in "decimal" rule

[koorchik]

Here is the example for reproduce:
http://livr-multi-playground.webbylab.com/#%7B%22rules%22%3A%22%7B%5Cn%20%20%20%20'test'%3A%20'decimal'%5Cn%7D%22%2C%22input%22%3A%22%7B%5Cn%20%20%20%20'test'%3A%20-3.00%5Cn%7D%22%7D

I have added additional tests to test suite - koorchik/LIVR@3bfd694

Here is an example, how it was fixed in JS implementation - koorchik/js-validator-livr@5e8dc21#diff-1e3604932255b8e9b4aba0a1c5f96ae9R35