py-protobuf: updated to 3.8.0

Protocol Buffers v3.8.0
Python
Changes implementation of Name() for enums that allow aliases in proto2 in Python to be in line with claims in C++ implementation (to return first value).
Added double_format option in text format printer.
Added iter and contains to extension dict
Added allow_unknown_field option in python text format parser
Fixed Timestamp.ToDatetime() loses precision issue
Support unknown field in text format printer.
Float field will be convert to inf if bigger than struct.unpack('f', b'\xff\xff\x7f\x7f')[0] which is about 3.4028234664e+38,
convert to -inf if smaller than -3.4028234664e+38
Allowed casting str->bytes in Message.setstate

(adam)