setup.py: use plyvel==1.2.0 instead of 1.0.5

[belikor]

As indicated in INSTALL.md, setting up the virtual environment and running make.

# 5.12.14-arch1-1 #1 SMP PREEMPT Thu, 01 Jul 2021 07:26:06 +0000 x86_64 GNU/Linux

python3.9 -m venv lbry-venv9
make install

The process errors in the compilation of plyvel.

ERROR: Command errored out with exit status 1:
     command: /opt/git/lbry-sdk/lbry-venv9/bin/python3.9 -u -c 'import io, os, sys, setuptools, tokenize; sys.argv[0] = '"'"'/tmp/pip-install-ne_ytn2l/plyvel_462f51d795a34180a99f8ad88be3ebc2/setup.py'"'"'; __file__='"'"'/tmp/pip-install-ne_ytn2l/plyvel_462f51d795a34180a99f8ad88be3ebc2/setup.py'"'"';f = getattr(tokenize, '"'"'open'"'"', open)(__file__) if os.path.exists(__file__) else io.StringIO('"'"'from setuptools import setup; setup()'"'"');code = f.read().replace('"'"'\r\n'"'"', '"'"'\n'"'"');f.close();exec(compile(code, __file__, '"'"'exec'"'"'))' install --record /tmp/pip-record-cylvo3wk/install-record.txt --single-version-externally-managed --compile --install-headers /opt/git/lbry-sdk/lbry-venv9/include/site/python3.9/plyvel

...
gcc -pthread -Wno-unused-result -Wsign-compare -DNDEBUG -g -fwrapv -O3 -Wall -march=x86-64 -mtune=generic -O3 -pipe -fno-plt -fno-semantic-interposition -march=x86-64 -mtune=generic -O3 -pipe -fno-plt -march=x86-64 -mtune=generic -O3 -pipe -fno-plt -fPIC -I/opt/git/lbry-sdk/lbry-venv9/include -I/usr/include/python3.9 -c plyvel/_plyvel.cpp -o build/temp.linux-x86_64-3.9/plyvel/_plyvel.o -Wall -g
    plyvel/_plyvel.cpp: In function ‘int __Pyx_modinit_type_init_code()’:
    plyvel/_plyvel.cpp:21100:34: error: ‘PyTypeObject’ {aka ‘struct _typeobject’} has no member named ‘tp_print’
    21100 |   __pyx_type_6plyvel_7_plyvel_DB.tp_print = 0;
          |                                  ^~~~~~~~

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To avoid this error, we can set plyvel==1.2.0 or plyvel==1.3.0 in setup.py. Then the installation completes fine.

I don't know if there is a particular reason for using plyvel==1.0.5 (July 17, 2018), as it is currently. This version compiles fine with Python 3.7 and 3.8, but only 3.7 truly works correctly (see #2769, #2145).

I tried plyvel==1.2.0 (January 22, 2020) because it's the version available in Ubuntu 20.04, and plyvel==1.3.0 (October 10, 2020) because it's the latest stable version available in Arch.

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If this is merged, then maybe we don't need to install libleveldb-dev, as proposed in #3349.

This fix is also included in #3205, so if #3205 is merged, this pull request is not needed. Otherwise this can be merged already.

[eukreign]

As already mentioned, #3205 already includes this fix, let's just wait for that to merge instead of doing this upgrade separately.