refactor stemmer : extract method normalize text
recoding rule 15 : menangkap -> tangkap
recoding rule 13 : memukul -> pukul
recoding rule 17 : mengupas -> kupas
recoding rule 26 : pemukul -> pukul
recoding rule 28 : penangkap -> tangkap
recoding rule 30 : pengupas -> kupas