remarshal: bump PyYAML dependency version to compile with python 3.7

[mdaniel]

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---

[fxcoudert]

@mdaniel can you explain what is the problem this PR is trying to fix? remarshal is building fine on macOS Sierra to Mojave.

[mdaniel]

$ brew install --build-from-source remarshal
# [...snip...]
Installing collected packages: PyYAML
  Created temporary directory: /private/tmp/pip-record-5etyjdar
  Running setup.py install for PyYAML: started
    Running command /usr/local/Cellar/remarshal/0.8.0_1/libexec/bin/python3.7 -u -c "import setuptools, tokenize;__file__='/private/tmp/pip-req-build-kuwuodp7/setup.py';f=getattr(tokenize, 'open', open)(__file__);code=f.read().replace('\r\n', '\n');f.close();exec(compile(code, __file__, 'exec'))" install --record /private/tmp/pip-record-5etyjdar/install-record.txt --single-version-externally-managed --compile --install-headers /usr/local/Cellar/remarshal/0.8.0_1/libexec/bin/../include/site/python3.7/PyYAML
    running install
    running build
    running build_py
    creating build
    creating build/lib.macosx-10.12-x86_64-3.7
    creating build/lib.macosx-10.12-x86_64-3.7/yaml
    copying lib3/yaml/__init__.py -> build/lib.macosx-10.12-x86_64-3.7/yaml
    copying lib3/yaml/composer.py -> build/lib.macosx-10.12-x86_64-3.7/yaml
    copying lib3/yaml/constructor.py -> build/lib.macosx-10.12-x86_64-3.7/yaml
    copying lib3/yaml/cyaml.py -> build/lib.macosx-10.12-x86_64-3.7/yaml
    copying lib3/yaml/dumper.py -> build/lib.macosx-10.12-x86_64-3.7/yaml
    copying lib3/yaml/emitter.py -> build/lib.macosx-10.12-x86_64-3.7/yaml
    copying lib3/yaml/error.py -> build/lib.macosx-10.12-x86_64-3.7/yaml
    copying lib3/yaml/events.py -> build/lib.macosx-10.12-x86_64-3.7/yaml
    copying lib3/yaml/loader.py -> build/lib.macosx-10.12-x86_64-3.7/yaml
    copying lib3/yaml/nodes.py -> build/lib.macosx-10.12-x86_64-3.7/yaml
    copying lib3/yaml/parser.py -> build/lib.macosx-10.12-x86_64-3.7/yaml
    copying lib3/yaml/reader.py -> build/lib.macosx-10.12-x86_64-3.7/yaml
    copying lib3/yaml/representer.py -> build/lib.macosx-10.12-x86_64-3.7/yaml
    copying lib3/yaml/resolver.py -> build/lib.macosx-10.12-x86_64-3.7/yaml
    copying lib3/yaml/scanner.py -> build/lib.macosx-10.12-x86_64-3.7/yaml
    copying lib3/yaml/serializer.py -> build/lib.macosx-10.12-x86_64-3.7/yaml
    copying lib3/yaml/tokens.py -> build/lib.macosx-10.12-x86_64-3.7/yaml
    running build_ext
    creating build/temp.macosx-10.12-x86_64-3.7
    checking if libyaml is compilable
    clang -Wno-unused-result -Wsign-compare -Wunreachable-code -fno-common -dynamic -DNDEBUG -g -fwrapv -O3 -Wall -I/usr/local/opt/python/Frameworks/Python.framework/Versions/3.7/include/python3.7m -c build/temp.macosx-10.12-x86_64-3.7/check_libyaml.c -o build/temp.macosx-10.12-x86_64-3.7/check_libyaml.o
    checking if libyaml is linkable
    clang build/temp.macosx-10.12-x86_64-3.7/check_libyaml.o -lyaml -o build/temp.macosx-10.12-x86_64-3.7/check_libyaml
    building '_yaml' extension
    creating build/temp.macosx-10.12-x86_64-3.7/ext
    clang -Wno-unused-result -Wsign-compare -Wunreachable-code -fno-common -dynamic -DNDEBUG -g -fwrapv -O3 -Wall -I/usr/local/opt/python/Frameworks/Python.framework/Versions/3.7/include/python3.7m -c ext/_yaml.c -o build/temp.macosx-10.12-x86_64-3.7/ext/_yaml.o
    ext/_yaml.c:24143:21: error: no member named 'exc_type' in 'struct _ts'
        *type = tstate->exc_type;
                ~~~~~~  ^
    ext/_yaml.c:24144:22: error: no member named 'exc_value' in 'struct _ts'; did you mean 'curexc_value'?

and then the error messages continue verbosely from there.

Since (to the very best of my knowledge) PyYAML 3.12 is backward compatible with Python 2.7, so it won't make your coincidentally successful builds any less successful, and for sure solves a situation that exists once brew info python became 3.7. Interestingly enough, /usr/local/bin/python does actually still point to ../Cellar/python@2/2.7.15_1/bin/python but I suspect strongly the depends_on "python" in remarshal is grabbing 3.7 because of the output of brew info python.

[fxcoudert]

@BrewTestBot test this please