Compile error when Python < 3.6

[fcojavmc]

Please, pre-check Python version to prevent this error. Thank you.

I have compiled using Python 3.4:

File "userver/plugins/external_deps/impl/cmake_generator.py", line 81

result: dict = {}
SyntaxError: invalid syntax
CMake Error at CMakeLists.txt:70 (message):
Generating cmake files failed with exit code: 1

[apolukhin]

That's quite an outdated Python :)

However, you have an interest in this feature, so we'll add support for it. Note that the feature has low priority, so PR are welcomed to speedup the things a little bit.