Currency verbalization can be bricked by environment locales

[RadekKazbundaAtMama]

On my local machine normalization of English currencies does not work, because by linux installation is set non US locales:

gruut -l en-us "\$10"
{"idx": 0, "text": "$10", "text_with_ws": "$10", "text_spoken": "$10", "par_idx": 0, "lang": "en-us", "voice": "", "words": [{"idx": 0, "text": "$10", "text_with_ws": "$10", "leading_ws": "", "trailing_ws": "", "sent_idx": 0, "par_idx": 0, "lang": "en-us", "voice": "", "pos": "NN", "phonemes": [], "is_major_break": false, "is_minor_break": false, "is_punctuation": false, "is_break": false, "is_spoken": true, "pause_before_ms": 0, "pause_after_ms": 0, "marks_before": null, "marks_after": null}], "pause_before_ms": 0, "pause_after_ms": 0, "marks_before": null, "marks_after": null}

If I set local LC_NUMERIC to en_US locale, then it will work. The problem is called by using default babel locale when configuring gruut. I can make a PR with fix.