Travis CI failing for Python 3.7.1 build

[alexlyttle]

Travis-Ci getting TypeError: Plain typing.NoReturn is not valid as type argument for the Python 3.7.1 Linux build of PR #257. I did some digging and this is a Python bug from 3.7.1. We should upgrade the Python version for this build as recommended by the linked issue. It has probably only just occurred due to an update in another package to make use of typing.NoReturn.

[alexlyttle]

Here is the fully traceback. Occurs when pbjam is imported

../../../virtualenv/python3.7.1/lib/python3.7/site-packages/py/_path/local.py:701: in pyimport
    __import__(modname)
pbjam/__init__.py:22: in <module>
    from .session import session
pbjam/session.py:53: in <module>
    from .star import star, _format_name
pbjam/star.py:20: in <module>
    from .peakbag import peakbag
pbjam/peakbag.py:9: in <module>
    import pymc3 as pm
../../../virtualenv/python3.7.1/lib/python3.7/site-packages/pymc3/__init__.py:39: in <module>
    __set_compiler_flags()
../../../virtualenv/python3.7.1/lib/python3.7/site-packages/pymc3/__init__.py:33: in __set_compiler_flags
    import theano
../../../virtualenv/python3.7.1/lib/python3.7/site-packages/theano/__init__.py:83: in <module>
    from theano import scalar, tensor
../../../virtualenv/python3.7.1/lib/python3.7/site-packages/theano/scalar/__init__.py:1: in <module>
    from .basic import *
../../../virtualenv/python3.7.1/lib/python3.7/site-packages/theano/scalar/basic.py:22: in <module>
    from theano import printing
../../../virtualenv/python3.7.1/lib/python3.7/site-packages/theano/printing.py:18: in <module>
    from theano.compile import Function, SharedVariable, debugmode
../../../virtualenv/python3.7.1/lib/python3.7/site-packages/theano/compile/__init__.py:1: in <module>
    from theano.compile.function.pfunc import Param, pfunc, rebuild_collect_shared
../../../virtualenv/python3.7.1/lib/python3.7/site-packages/theano/compile/function/__init__.py:7: in <module>
    from theano.compile.function.pfunc import pfunc
../../../virtualenv/python3.7.1/lib/python3.7/site-packages/theano/compile/function/pfunc.py:9: in <module>
    from theano.compile.function.types import UnusedInputError, orig_function
../../../virtualenv/python3.7.1/lib/python3.7/site-packages/theano/compile/function/types.py:20: in <module>
    from theano.compile.io import In, SymbolicInput, SymbolicOutput
../../../virtualenv/python3.7.1/lib/python3.7/site-packages/theano/compile/io.py:9: in <module>
    from theano.link.basic import Container
../../../virtualenv/python3.7.1/lib/python3.7/site-packages/theano/link/basic.py:8: in <module>
    from theano.link.utils import gc_helper, map_storage, raise_with_op, streamline
../../../virtualenv/python3.7.1/lib/python3.7/site-packages/theano/link/utils.py:135: in <module>
    ) -> typing.Callable[[], typing.NoReturn]:
/opt/python/3.7.1/lib/python3.7/typing.py:755: in __getitem__
    return self.__getitem_inner__(params)
/opt/python/3.7.1/lib/python3.7/typing.py:251: in inner
    return func(*args, **kwds)
/opt/python/3.7.1/lib/python3.7/typing.py:774: in __getitem_inner__
    result = _type_check(result, msg)
/opt/python/3.7.1/lib/python3.7/typing.py:135: in _type_check
    raise TypeError(f"Plain {arg} is not valid as type argument")
E   TypeError: Plain typing.NoReturn is not valid as type argument