Cannot use psycopg2 2.7.5 on mac builds of beat-devel

For some weird reason, I had to pin psycopg2 to version 2.6.2 on macOS instead of the latest available on the conda channel, which is 2.7.5. My preliminary analysis indicates some incompatibility with openssl 1.0.2? vs 1.1.1a.

@amohammadi: do you have any idea why this is the case?