Remove unwanted characters from the input

[andresindlp]

When the data given is for example "45.0 ºC" it doesn't work.

With value_str = value_str.replace(/[^0-9.]/g, '');, everything but numbers and the dot are removed, leaving a clean output.

[metbosch]

Thanks for the contribution. I would publish a new version in npmjs soon with this changes.