ph_english: use /i/ as the IPA transcription of i

The i phoneme is used for the reduced i sound in e.g. happy
(/h'api/). Thus, the following words contrast:

    word   eSpeak   IPA
    happy  /h'api/  /hˈapi/
    been   /b'i:n/  /bˈiːn/
    bin    /b'In/   /bˈɪn/

Before this change, /h'api/ would be transcribed in IPA as /hˈapɪ/
which is wrong. After this change, it is transcribed correctly.