Update depthai-api (python3_exact_version)

[alex-luxonis]

See PR luxonis/depthai-python#28

With multiple python3 versions installed (side by side, or within Conda environments),
CMake's find_package always returned the latest (e.g. even if we specify 3.6, if 3.7 is found, it is used instead).
With an older python3 interpreter enabled as default, this was causing a wrong lib to be built, not the one expected by the selected python3 interpreter.

However, find_package has an option EXACT that would solve the above issue, but we don't want to hardcode a specific version.
We query the version from the python3 interpreter and pass it to find_package.

[Luxonis-Brandon]

Tested on Mac and works fine. I'd say this is good to go.

[SzabolcsGergely]

lgtm