Update integer.py to parse integers in exp notation

[msgr0]

When integer value is given in exponential notation, python doesn't parse it as an integer resulting in not validating the gfa file. Casting to float and then to int resolves the issue.

[msgr0]

example of given error on a skesa bacterial assembly .gfa file

gfapy.error.FormatError: Field: KC
  Datatype: i
  Content: 1.44333e+06
  invalid literal for int() with base 10: '1.44333e+06':the string does not represent a valid integer