Make regex closer to what backend allows.  Fix issue where `doi:` was allowed as prefix in doi field.
Make regex closer to what backend allows.  Fix issue where `doi:` was allowed as prefix in doi field.

(should have a suffix rule, but going for consistency over accuracy)

[#prep-117]

hmoco/ember-preprints,caneruguz/ember-preprints,laurenrevere/ember-preprints,laurenrevere/ember-preprints,baylee-d/ember-preprints,baylee-d/ember-preprints,pattisdr/ember-preprints,CenterForOpenScience/ember-preprints,CenterForOpenScience/ember-preprints,caneruguz/ember-preprints,pattisdr/ember-preprints,hmoco/ember-preprints