Build using newer manylinux image.

[jamadden]

And update macOS python to 2.7.17 to try to fix uploads.

[mgedmin]

Are we ready to drop manylinux1 wheels?

Maybe we should build both manylinux1 and manylinux2010?

[jamadden]

That's the beauty part: these are still manylinux1 wheels, just built with a much more capable toolchain:

+ for whl in 'wheelhouse/BTrees*.whl'
+ auditwheel repair wheelhouse/BTrees-4.6.2.dev0-cp36-cp36m-linux_x86_64.whl -w /io/wheelhouse/
INFO:auditwheel:Repairing BTrees-4.6.2.dev0-cp36-cp36m-linux_x86_64.whl
INFO:auditwheel:Previous filename tags: linux_x86_64
INFO:auditwheel:New filename tags: manylinux2010_x86_64
INFO:auditwheel:Previous WHEEL info tags: cp36-cp36m-linux_x86_64
INFO:auditwheel:New WHEEL info tags: cp36-cp36m-manylinux2010_x86_64
INFO:auditwheel:Wheel is eligible for a higher priority tag. 
     You requested manylinux2010_x86_64 but I have found this wheel 
     is eligible for manylinux1_x86_64.
INFO:auditwheel:Previous filename tags: linux_x86_64
INFO:auditwheel:New filename tags: manylinux1_x86_64
INFO:auditwheel:Previous WHEEL info tags: cp36-cp36m-linux_x86_64
INFO:auditwheel:New WHEEL info tags: cp36-cp36m-manylinux1_x86_64
INFO:auditwheel:
Fixed-up wheel written to 
     /io/wheelhouse/BTrees-4.6.2.dev0-cp36-cp36m-manylinux1_x86_64.whl

[mgedmin]

Oh, excellent!