Update Ile-de-France Mobilité feed name to include IDFM

Problem: 
- The long name is written: **Î**le-de-France Mobilité**s**
- Île-de-France Mobilités is commonly called IDFM

Feed: https://mobilitydatabase.org/feeds/gtfs/mdb-1026

Task: Rename to _Île-de-France Mobilités (IDFM)_ so it's easier to find. 
Similar to the name of [this feed](https://mobilitydatabase.org/feeds/gtfs/mdb-1085).