ijson breaking change in 2.5

[luizirber]

FYI: ijson 2.5 breaks our tests (master is currently broken).

I'm pinning it in 2d0e297, but need to investigate a more permanent fix (or drop ijson and do the parsing in Rust, wink wink).

Relevant issue: ICRAR/ijson#13

[ctb]

so, we're not actually using ijson anywhere any more. But it's in the docs...

% git grep ijson
README.md:requirements are screed and ijson, together with a Rust environment (for the
doc/developer.md:requirements are screed and ijson, together with a Rust environment (for the
doc/release.md:python -m pip install screed pytest numpy matplotlib scipy khmer ijson bam2fasta deprecation cffi
tests/test_deprecated.py:    # ijson requires a file in binary mode or bytes,

[ctb]

removing from docs in #1140, but in any case this issue is no longer relevant :)