RNG links to reference.cs50.net need slight fix

[curiouskiwi]

The 2 links to reference.cs50.net (in the Getting Ready) section currently show:

https://reference.cs50.net/stdlib.h/srand48 and
https://reference.cs50.net/stdlib.h/drand48

These should be:

https://reference.cs50.net/stdlib/srand48
https://reference.cs50.net/stdlib/drand48

(without the .h in the folder name)

From here:
http://docs.cs50.net/2016/x/ap/problems/rng/rng.html

(reported by a student)

[dmalan]

Thanks! Want to submit a PR?

[curiouskiwi]

Have done so. Closing.