Fix compilation in OSX

[codeadict]

Fixes #1391

This PR adds:

• Temporarily upgraded eleveldb dependency to compile in OSX.

• Fix for OSX compilation due to recent Homebrew changes that added OpenSSL 1.1 and deprecated 1.0, this new way will ensure that compilation always use the latest OpenSSL installed by Homebrew, making it more resilient to changes. Still could be issues on systems that had the previous OpenSSL version and static libraries are still hanging around (The error looks like dyld: Library not loaded: /usr/local/opt/openssl@1.1/lib/libcrypto.1.0.0.dylib), the best on this case is to run:

$ brew update
$ brew uninstall --ignore-dependencies openssl
$ brew install openssl

[codeadict]

@ioolkos @dergraf this is the new branch as the other got messed up rebasing.

[ioolkos]

Okay, thanks :)