Fix when a number has a comma in it using the wrong number for calculations

If you initialize calculadora with the default settings and input 1000+150 [enter] it displays 1,150
Then if you press -100 [enter] it will parse the float incorrectly because of the thousands separator in 1,150 and give the improper answer.  

This fix simply removes commas before the float is parsed 

This is a great project!  Thank you :-)