Prevent new instruments being created with spaces in the prefix

[HayleyMills]

[beckyoldroyd]

Addressed and on production

[beckyoldroyd]

It looks like it doesn't allow me to create an instrument with a space in the prefix as I get an error message, but when I go to the Instruments page I can see it (see "test_ space" here https://closer-archivist.herokuapp.com/instruments/).

I can't view it, or edit it on Admin > Instruments to delete it.

[beckyoldroyd]

@simonreed see the comment above