Fix tests for new versions of jest and other packages: * The snapshots used \\ for a single backslash, but this is no longer recognised, so they have all been replaced by single backslashes * The newer versions of woff2 and brotli we are using produce a different woff2 file, so the MD5 hash in the test has been updated to reflect this
Modify test scripts to use available files only Also, the current version of read-chunk seems to be incompatible with these test scripts, so we simply replace it with fs.
