Update robopaint.fr.json

opt4 correction to match en-US version

"filltitle": "Remplissage",
      "filltype": {
        "title": "Type:",
        "opt0": "Tout droit",
        "opt1": "Ligne triangulaire",
        "opt2": "Sinusoïde",
        "opt3": "Spirale",
        "opt4": "n'importe quoi"
},