Update the yamlStyleFloat regex for special case.

[howbazaar]

Fixes #157 by updating the regex for float matching.

Instead of allowing mantissa to be any 0-9 sequence, this change means it must be either 0, or not start with a zero.

[gabriel-samfira]

Shouldn't this be:

// the sign of what follows after "[eE]" should be optional. 
var yamlStyleFloat = regexp.MustCompile(`^[-+]?(0|[1-9][0-9]*)?(\.[0-9]+)?([eE][-+]?[0-9]+)?$`)

to allow:

floats := []string{
   "2.2e11",
   "2.2e+11", // same as above, but with an explicit sign
   "2.2e-11",
}

?

[howbazaar]

Well the spec says that all exponents must have explicit sign.