URI schemes containing digits cause parse error

[balhoff]

I have some RDF data autoconverted from a Neo4j database. It creates URIs using a neo4j:// scheme like this:

<neo4j://graph.individuals#n4ind:389638>  <neo4j://graph.schema#knows>  <neo4j://graph.individuals#145613> .

Using this data with Comunica throws an error in SPARQL query parsing:

Cannot resolve relative IRI neo4j://graph.individuals#105029 because no base IRI was set.

It looks like this is caused by the regex here:

SPARQL.js/lib/sparql.jison

Line 60 in ebde86c

if (/^[a-z]+:/i.test(iri))

which only allows letters. I haven't found anything that says a scheme can't contain a digit, and Wikipedia also mentions s3:// as a commonly used scheme.