Function invert

invert(name): IntervalName
Get the inversion (https://en.wikipedia.org/wiki/Inversion_(music)#Intervals) of an interval.
Parameters
- name: string
Returns IntervalName
the inverted interval
Function
Example
```
Interval.invert("3m") // => "6M"
Interval.invert("2M") // => "7m"
```
- Defined in src/music/interval/index.ts:93