pip install pyfst fails on python 3.7

OSX Mojave, python 3.7.1
did the following:
- installed openfst 1.5.4
- `$ export CFLAGS="-std=c++11 -stdlib=libc++ -mmacosx-version-min=10.7" && export CPATH="/usr/local/include"`
- `pip install pyfst`

Had lots of compilation errors. Downgrading to python 3.6.4 solved the issue.