Update mochiweb version to prevent build failure

[blacklight]

The build process currently fails with the following trace:

===> Compiling src/mochiweb_multipart.erl failed
src/mochiweb_multipart.erl:278:13: syntax error before: ','
src/mochiweb_multipart.erl:331:9: syntax error before: ','

src/mochiweb_multipart.erl:186:5: function feed_mp/2 undefined

src/mochiweb_multipart.erl:191:1: Warning: function parse_headers/1 is unused
src/mochiweb_multipart.erl:194:1: Warning: function parse_headers/2 is unused
src/mochiweb_multipart.erl:202:1: Warning: function split_header/1 is unused
src/mochiweb_multipart.erl:217:1: Warning: function read_more/1 is unused
src/mochiweb_multipart.erl:300:1: Warning: function find_in_binary/2 is unused
src/mochiweb_multipart.erl:312:1: Warning: function partial_find/4 is unused

That's apparently because the project uses an old version of Mochiweb (from 2021).