Convert does not work on lü, nü, lüe

[daddehs1]

Expected Behavior

On converting hanzi such as 绿, 女, or 略, the expected outputs would be:

['ㄌㄩˋ']
[ ['ㄋㄩˇ', 'ㄖㄨˇ' ] ]
['ㄌㄩㄝˋ']

Current Behavior

Current outputs for 绿, 女, or 略 are, respectively:

[ 'undefined`' ]
[ [ 'undefinedˇ', 'ㄖㄨˇ' ] ]
[ 'undefined`' ]

Notes:

1. 女 has a secondary pronunciation (pinyin: ru3, zhuyin: ㄖㄨˇ) which behaves as expected
   The issue only occurs on the primary pronunciation which contains (pinyin: ü, zhuyin:ㄩ)

2. The issue does not occur when converting hanzi which contain (pinyin: ü, zhuyin:ㄩ) that do not also contain (pinyin: r, zhuyin:ㄖ) or (pinyin: n, zhuyin:ㄋ)
   e.g. converting 与, 月, 元, 需, 学, 选, 句, 觉, 卷, 去, 却, 全 functions as expected.
   This may suggest that the issue lies with the pinyin character "ü", as the list of characters above are all written with a "u" in pinyin although the pronunciation is in actuality "ü"

Steps to Reproduce

1. install node package hanzi-to-zhuyin
2. execute the following code:

const convert = require('hanzi-to-zhuyin');
convert("绿").then(console.log)