Just variations of transliteration. There is no difference in meaning or usage, as Majestic-san wrote. The former one デジタル "dejitaru" is still more commonly used, I think.
Many variations like that exist in loanwords.
e.g.
December: ディッセンバー "dissenbā" / ディセンバー "disenbā"
tip: チップ "chippu" / ティップ "tippu"
diamond: ダイアモンド "daiamondo" / ダイヤモンド "daiyamondo"
foul: ファール "fāru" / ファウル "fauru"