Can't validate PSI-XML 3.0

[julie-sullivan]

When I try to validate a file using the validator, I get this error:

Syntax warning : org.xml.sax.SAXParseException; lineNumber: 396; columnNumber: 117; 
schema_reference.4: Failed to read schema document 'https://raw.githubusercontent.com/HUPO-
PSI/miXML/master/3.0/src/MIF300.xsd', because 1) could not find the document; 2) the document could 
not be read; 3) the root element of the document is not <xsd:schema>. at 
org.apache.xerces.util.ErrorHandlerWrapper.createSAXParseException(Unknown Source) at 
org.apache.xerces.util.ErrorHandlerWrapper.warning(Unknown Source) at 
org.apache.xerces.impl.XMLErrorReporter.reportError(Unknown Source) at 
...

I tried two Homo sapiens file, e.g. ftp.ebi.ac.uk/pub/databases/intact/complex/current/psi30/human/cst_human.xml